diff --git a/ethcore/src/account.rs b/ethcore/src/account.rs
index 7ba213393..5e0dc335a 100644
--- a/ethcore/src/account.rs
+++ b/ethcore/src/account.rs
@@ -51,8 +51,6 @@ impl Account {
 		}
 	}
 
-	#[cfg(test)]
-	#[cfg(feature = "json-tests")]
 	/// General constructor.
 	pub fn from_pod(pod: PodAccount) -> Account {
 		Account {
diff --git a/ethcore/src/client/client.rs b/ethcore/src/client/client.rs
index 3ddf7018a..97f8dd5a4 100644
--- a/ethcore/src/client/client.rs
+++ b/ethcore/src/client/client.rs
@@ -37,7 +37,7 @@ use filter::Filter;
 use log_entry::LocalizedLogEntry;
 use block_queue::{BlockQueue, BlockQueueInfo};
 use blockchain::{BlockChain, BlockProvider, TreeRoute, ImportRoute};
-use client::{BlockID, TransactionID, UncleID, TraceId, ClientConfig, BlockChainClient, MiningBlockChainClient, TraceFilter};
+use client::{BlockID, TransactionID, UncleID, TraceId, ClientConfig, BlockChainClient, MiningBlockChainClient, TraceFilter, CallAnalytics};
 use client::Error as ClientError;
 use env_info::EnvInfo;
 use executive::{Executive, Executed, TransactOptions, contract_address};
@@ -429,14 +429,14 @@ impl<V> Client<V> where V: Verifier {
 			TransactionID::Hash(ref hash) => self.chain.transaction_address(hash),
 			TransactionID::Location(id, index) => Self::block_hash(&self.chain, id).map(|hash| TransactionAddress {
 				block_hash: hash,
-				index: index
+				index: index,
 			})
 		}
 	}
 }
 
 impl<V> BlockChainClient for Client<V> where V: Verifier {
-	fn call(&self, t: &SignedTransaction, vm_tracing: bool) -> Result<Executed, ExecutionError> {
+	fn call(&self, t: &SignedTransaction, analytics: CallAnalytics) -> Result<Executed, ExecutionError> {
 		let header = self.block_header(BlockID::Latest).unwrap();
 		let view = HeaderView::new(&header);
 		let last_hashes = self.build_last_hashes(view.hash());
@@ -456,11 +456,21 @@ impl<V> BlockChainClient for Client<V> where V: Verifier {
 			ExecutionError::TransactionMalformed(message)
 		}));
 		let balance = state.balance(&sender);
-		// give the sender a decent balance
-		state.sub_balance(&sender, &balance);
-		state.add_balance(&sender, &(U256::from(1) << 200));
-		let options = TransactOptions { tracing: false, vm_tracing: vm_tracing, check_nonce: false };
-		Executive::new(&mut state, &env_info, self.engine.deref().deref(), &self.vm_factory).transact(t, options)
+		let needed_balance = t.value + t.gas * t.gas_price;
+		if balance < needed_balance {
+			// give the sender a sufficient balance
+			state.add_balance(&sender, &(needed_balance - balance));
+		}
+		let options = TransactOptions { tracing: false, vm_tracing: analytics.vm_tracing, check_nonce: false };
+		let mut ret = Executive::new(&mut state, &env_info, self.engine.deref().deref(), &self.vm_factory).transact(t, options);
+		
+		// TODO gav move this into Executive.
+		if analytics.state_diffing {
+			if let Ok(ref mut x) = ret {
+				x.state_diff = Some(state.diff_from(self.state()));
+			}
+		}
+		ret
 	}
 
 	fn vm_factory(&self) -> &EvmFactory {
@@ -505,7 +515,6 @@ impl<V> BlockChainClient for Client<V> where V: Verifier {
 		self.state_at(id).map(|s| s.nonce(address))
 	}
 
-
 	fn block_hash(&self, id: BlockID) -> Option<H256> {
 		Self::block_hash(&self.chain, id)
 	}
diff --git a/ethcore/src/client/mod.rs b/ethcore/src/client/mod.rs
index 84eea7494..0dffb1a1c 100644
--- a/ethcore/src/client/mod.rs
+++ b/ethcore/src/client/mod.rs
@@ -49,6 +49,15 @@ use evm::Factory as EvmFactory;
 use miner::{TransactionImportResult};
 use error::Error as EthError;
 
+/// Options concerning what analytics we run on the call.
+#[derive(Eq, PartialEq, Default, Clone, Copy, Debug)]
+pub struct CallAnalytics {
+	/// Make a VM trace.
+	pub vm_tracing: bool,
+	/// Make a diff.
+	pub state_diffing: bool,
+}
+
 /// Blockchain database client. Owns and manages a blockchain and a block queue.
 pub trait BlockChainClient : Sync + Send {
 	/// Get raw block header data by block id.
@@ -158,7 +167,7 @@ pub trait BlockChainClient : Sync + Send {
 
 	/// Makes a non-persistent transaction call.
 	// TODO: should be able to accept blockchain location for call.
-	fn call(&self, t: &SignedTransaction, vm_tracing: bool) -> Result<Executed, ExecutionError>;
+	fn call(&self, t: &SignedTransaction, analytics: CallAnalytics) -> Result<Executed, ExecutionError>;
 
 	/// Returns EvmFactory.
 	fn vm_factory(&self) -> &EvmFactory;
diff --git a/ethcore/src/client/test_client.rs b/ethcore/src/client/test_client.rs
index f3768d0a6..17905a905 100644
--- a/ethcore/src/client/test_client.rs
+++ b/ethcore/src/client/test_client.rs
@@ -20,7 +20,7 @@ use std::sync::atomic::{AtomicUsize, Ordering as AtomicOrder};
 use util::*;
 use transaction::{Transaction, LocalizedTransaction, SignedTransaction, Action};
 use blockchain::TreeRoute;
-use client::{BlockChainClient, MiningBlockChainClient, BlockChainInfo, BlockStatus, BlockID, TransactionID, UncleID, TraceId, TraceFilter, LastHashes};
+use client::{BlockChainClient, MiningBlockChainClient, BlockChainInfo, BlockStatus, BlockID, TransactionID, UncleID, TraceId, TraceFilter, LastHashes, CallAnalytics};
 use header::{Header as BlockHeader, BlockNumber};
 use filter::Filter;
 use log_entry::LocalizedLogEntry;
@@ -251,7 +251,7 @@ impl MiningBlockChainClient for TestBlockChainClient {
 }
 
 impl BlockChainClient for TestBlockChainClient {
-	fn call(&self, _t: &SignedTransaction, _vm_tracing: bool) -> Result<Executed, ExecutionError> {
+	fn call(&self, _t: &SignedTransaction, _analytics: CallAnalytics) -> Result<Executed, ExecutionError> {
 		Ok(self.execution_result.read().unwrap().clone().unwrap())
 	}
 
diff --git a/ethcore/src/executive.rs b/ethcore/src/executive.rs
index 43864ee9e..fdc1c7d18 100644
--- a/ethcore/src/executive.rs
+++ b/ethcore/src/executive.rs
@@ -450,6 +450,7 @@ impl<'a> Executive<'a> {
 					output: output,
 					trace: trace,
 					vm_trace: vm_trace,
+					state_diff: None,
 				})
 			},
 			_ => {
@@ -463,6 +464,7 @@ impl<'a> Executive<'a> {
 					output: output,
 					trace: trace,
 					vm_trace: vm_trace,
+					state_diff: None,
 				})
 			},
 		}
diff --git a/ethcore/src/json_tests/state.rs b/ethcore/src/json_tests/state.rs
index 5cc611491..5307fb319 100644
--- a/ethcore/src/json_tests/state.rs
+++ b/ethcore/src/json_tests/state.rs
@@ -16,8 +16,7 @@
 
 use super::test_common::*;
 use tests::helpers::*;
-use pod_state::*;
-use state_diff::*;
+use pod_state::{self, PodState};
 use ethereum;
 use ethjson;
 
@@ -71,7 +70,7 @@ pub fn json_chain_test(json_data: &[u8], era: ChainEra) -> Vec<String> {
 					let our_post = state.to_pod();
 					println!("Got:\n{}", our_post);
 					println!("Expect:\n{}", post);
-					println!("Diff ---expect -> +++got:\n{}", StateDiff::diff_pod(&post, &our_post));
+					println!("Diff ---expect -> +++got:\n{}", pod_state::diff_pod(&post, &our_post));
 				}
 
 				if let Ok(r) = res {
diff --git a/ethcore/src/lib.rs b/ethcore/src/lib.rs
index cb7942f23..f69048a95 100644
--- a/ethcore/src/lib.rs
+++ b/ethcore/src/lib.rs
@@ -119,8 +119,6 @@ mod basic_types;
 #[macro_use] mod evm;
 mod env_info;
 mod pod_account;
-mod account_diff;
-mod state_diff;
 mod state;
 mod account;
 mod account_db;
diff --git a/ethcore/src/miner/miner.rs b/ethcore/src/miner/miner.rs
index 46b5ae733..5dc3864c3 100644
--- a/ethcore/src/miner/miner.rs
+++ b/ethcore/src/miner/miner.rs
@@ -20,10 +20,9 @@ use std::sync::atomic::AtomicBool;
 use util::*;
 use util::keys::store::{AccountProvider};
 use views::{BlockView, HeaderView};
-use client::{MiningBlockChainClient, BlockID};
+use client::{MiningBlockChainClient, Executive, Executed, EnvInfo, TransactOptions, BlockChainClient, BlockID, CallAnalytics};
 use block::{ClosedBlock, IsBlock};
 use error::*;
-use client::{Executive, Executed, EnvInfo, TransactOptions};
 use transaction::SignedTransaction;
 use receipt::{Receipt};
 use spec::Spec;
@@ -251,11 +250,13 @@ impl MinerService for Miner {
 		}
 	}
 
-	fn call(&self, chain: &MiningBlockChainClient, t: &SignedTransaction, vm_tracing: bool) -> Result<Executed, ExecutionError> {
+	fn call(&self, chain: &MiningBlockChainClient, t: &SignedTransaction, analytics: CallAnalytics) -> Result<Executed, ExecutionError> {
 		let sealing_work = self.sealing_work.lock().unwrap();
 		match sealing_work.peek_last_ref() {
 			Some(work) => {
 				let block = work.block();
+
+				// TODO: merge this code with client.rs's fn call somwhow.
 				let header = block.header();
 				let last_hashes = chain.last_hashes();
 				let env_info = EnvInfo {
@@ -274,16 +275,24 @@ impl MinerService for Miner {
 					ExecutionError::TransactionMalformed(message)
 				}));
 				let balance = state.balance(&sender);
-				// give the sender max balance
-				state.sub_balance(&sender, &balance);
-				state.add_balance(&sender, &U256::max_value());
-				let options = TransactOptions { tracing: false, vm_tracing: vm_tracing, check_nonce: false };
-
-				// TODO: use vm_trace here.
-				Executive::new(&mut state, &env_info, self.engine(), chain.vm_factory()).transact(t, options)
+				let needed_balance = t.value + t.gas * t.gas_price;
+				if balance < needed_balance {
+					// give the sender a sufficient balance
+					state.add_balance(&sender, &(needed_balance - balance));
+				}
+				let options = TransactOptions { tracing: false, vm_tracing: analytics.vm_tracing, check_nonce: false };
+				let mut ret = Executive::new(&mut state, &env_info, self.engine(), chain.vm_factory()).transact(t, options);
+				
+				// TODO gav move this into Executive.
+				if analytics.state_diffing {
+					if let Ok(ref mut x) = ret {
+						x.state_diff = Some(state.diff_from(block.state().clone()));
+					}
+				}
+				ret
 			},
 			None => {
-				chain.call(t, vm_tracing)
+				chain.call(t, analytics)
 			}
 		}
 	}
diff --git a/ethcore/src/miner/mod.rs b/ethcore/src/miner/mod.rs
index 8165dfbba..71727f51d 100644
--- a/ethcore/src/miner/mod.rs
+++ b/ethcore/src/miner/mod.rs
@@ -51,7 +51,7 @@ pub use self::external::{ExternalMiner, ExternalMinerService};
 
 use std::collections::BTreeMap;
 use util::{H256, U256, Address, Bytes};
-use client::{MiningBlockChainClient, Executed};
+use client::{MiningBlockChainClient, Executed, CallAnalytics};
 use block::ClosedBlock;
 use receipt::Receipt;
 use error::{Error, ExecutionError};
@@ -148,7 +148,7 @@ pub trait MinerService : Send + Sync {
 	fn balance(&self, chain: &MiningBlockChainClient, address: &Address) -> U256;
 
 	/// Call into contract code using pending state.
-	fn call(&self, chain: &MiningBlockChainClient, t: &SignedTransaction, vm_tracing: bool) -> Result<Executed, ExecutionError>;
+	fn call(&self, chain: &MiningBlockChainClient, t: &SignedTransaction, analytics: CallAnalytics) -> Result<Executed, ExecutionError>;
 
 	/// Get storage value in pending state.
 	fn storage_at(&self, chain: &MiningBlockChainClient, address: &Address, position: &H256) -> H256;
diff --git a/ethcore/src/pod_account.rs b/ethcore/src/pod_account.rs
index 65146296a..d04833cab 100644
--- a/ethcore/src/pod_account.rs
+++ b/ethcore/src/pod_account.rs
@@ -18,6 +18,7 @@ use util::*;
 use account::*;
 use account_db::*;
 use ethjson;
+use types::account_diff::*;
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 /// An account, expressed as Plain-Old-Data (hence the name).
@@ -106,17 +107,58 @@ impl fmt::Display for PodAccount {
 	}
 }
 
+/// Determine difference between two optionally existant `Account`s. Returns None
+/// if they are the same.
+pub fn diff_pod(pre: Option<&PodAccount>, post: Option<&PodAccount>) -> Option<AccountDiff> {
+	match (pre, post) {
+		(None, Some(x)) => Some(AccountDiff {
+			balance: Diff::Born(x.balance),
+			nonce: Diff::Born(x.nonce),
+			code: Diff::Born(x.code.clone()),
+			storage: x.storage.iter().map(|(k, v)| (k.clone(), Diff::Born(v.clone()))).collect(),
+		}),
+		(Some(x), None) => Some(AccountDiff {
+			balance: Diff::Died(x.balance),
+			nonce: Diff::Died(x.nonce),
+			code: Diff::Died(x.code.clone()),
+			storage: x.storage.iter().map(|(k, v)| (k.clone(), Diff::Died(v.clone()))).collect(),
+		}),
+		(Some(pre), Some(post)) => {
+			let storage: Vec<_> = pre.storage.keys().merge(post.storage.keys())
+				.filter(|k| pre.storage.get(k).unwrap_or(&H256::new()) != post.storage.get(k).unwrap_or(&H256::new()))
+				.collect();
+			let r = AccountDiff {
+				balance: Diff::new(pre.balance, post.balance),
+				nonce: Diff::new(pre.nonce, post.nonce),
+				code: Diff::new(pre.code.clone(), post.code.clone()),
+				storage: storage.into_iter().map(|k|
+					(k.clone(), Diff::new(
+						pre.storage.get(&k).cloned().unwrap_or_else(H256::new),
+						post.storage.get(&k).cloned().unwrap_or_else(H256::new)
+					))).collect(),
+			};
+			if r.balance.is_same() && r.nonce.is_same() && r.code.is_same() && r.storage.is_empty() {
+				None
+			} else {
+				Some(r)
+			}
+		},
+		_ => None,
+	}
+}
+
+
 #[cfg(test)]
 mod test {
 	use common::*;
-	use account_diff::*;
-	use super::*;
+	use types::account_diff::*;
+	use super::{PodAccount, diff_pod};
 
 	#[test]
 	fn existence() {
 		let a = PodAccount{balance: 69.into(), nonce: 0.into(), code: vec![], storage: map![]};
-		assert_eq!(AccountDiff::diff_pod(Some(&a), Some(&a)), None);
-		assert_eq!(AccountDiff::diff_pod(None, Some(&a)), Some(AccountDiff{
+		assert_eq!(diff_pod(Some(&a), Some(&a)), None);
+		assert_eq!(diff_pod(None, Some(&a)), Some(AccountDiff{
 			balance: Diff::Born(69.into()),
 			nonce: Diff::Born(0.into()),
 			code: Diff::Born(vec![]),
@@ -128,7 +170,7 @@ mod test {
 	fn basic() {
 		let a = PodAccount{balance: 69.into(), nonce: 0.into(), code: vec![], storage: map![]};
 		let b = PodAccount{balance: 42.into(), nonce: 1.into(), code: vec![], storage: map![]};
-		assert_eq!(AccountDiff::diff_pod(Some(&a), Some(&b)), Some(AccountDiff {
+		assert_eq!(diff_pod(Some(&a), Some(&b)), Some(AccountDiff {
 			balance: Diff::Changed(69.into(), 42.into()),
 			nonce: Diff::Changed(0.into(), 1.into()),
 			code: Diff::Same,
@@ -140,7 +182,7 @@ mod test {
 	fn code() {
 		let a = PodAccount{balance: 0.into(), nonce: 0.into(), code: vec![], storage: map![]};
 		let b = PodAccount{balance: 0.into(), nonce: 1.into(), code: vec![0], storage: map![]};
-		assert_eq!(AccountDiff::diff_pod(Some(&a), Some(&b)), Some(AccountDiff {
+		assert_eq!(diff_pod(Some(&a), Some(&b)), Some(AccountDiff {
 			balance: Diff::Same,
 			nonce: Diff::Changed(0.into(), 1.into()),
 			code: Diff::Changed(vec![], vec![0]),
@@ -162,7 +204,7 @@ mod test {
 			code: vec![],
 			storage: map_into![1 => 1, 2 => 3, 3 => 0, 5 => 0, 7 => 7, 8 => 0, 9 => 9]
 		};
-		assert_eq!(AccountDiff::diff_pod(Some(&a), Some(&b)), Some(AccountDiff {
+		assert_eq!(diff_pod(Some(&a), Some(&b)), Some(AccountDiff {
 			balance: Diff::Same,
 			nonce: Diff::Same,
 			code: Diff::Same,
diff --git a/ethcore/src/pod_state.rs b/ethcore/src/pod_state.rs
index d9d0cf764..76dac214b 100644
--- a/ethcore/src/pod_state.rs
+++ b/ethcore/src/pod_state.rs
@@ -17,7 +17,8 @@
 //! State of all accounts in the system expressed in Plain Old Data.
 
 use util::*;
-use pod_account::*;
+use pod_account::{self, PodAccount};
+use types::state_diff::StateDiff;
 use ethjson;
 
 /// State of all accounts in the system expressed in Plain Old Data.
@@ -29,7 +30,6 @@ impl PodState {
 	pub fn new() -> PodState { Default::default() }
 
 	/// Contruct a new object from the `m`.
-	#[cfg(test)]
 	pub fn from(m: BTreeMap<Address, PodAccount>) -> PodState { PodState(m) }
 
 	/// Get the underlying map.
@@ -41,8 +41,6 @@ impl PodState {
 	}
 
 	/// Drain object to get the underlying map.
-	#[cfg(test)]
-	#[cfg(feature = "json-tests")]
 	pub fn drain(self) -> BTreeMap<Address, PodAccount> { self.0 }
 }
 
@@ -72,3 +70,83 @@ impl fmt::Display for PodState {
 	}
 }
 
+/// Calculate and return diff between `pre` state and `post` state.
+pub fn diff_pod(pre: &PodState, post: &PodState) -> StateDiff {
+	StateDiff(pre.get().keys().merge(post.get().keys()).filter_map(|acc| pod_account::diff_pod(pre.get().get(acc), post.get().get(acc)).map(|d|(acc.clone(), d))).collect())
+}
+
+#[cfg(test)]
+mod test {
+	use common::*;
+	use types::state_diff::*;
+	use types::account_diff::*;
+	use pod_account::PodAccount;
+	use super::PodState;
+
+	#[test]
+	fn create_delete() {
+		let a = PodState::from(map![ 1.into() => PodAccount::new(69.into(), 0.into(), vec![], map![]) ]);
+		assert_eq!(super::diff_pod(&a, &PodState::new()), StateDiff(map![
+			1.into() => AccountDiff{
+				balance: Diff::Died(69.into()),
+				nonce: Diff::Died(0.into()),
+				code: Diff::Died(vec![]),
+				storage: map![],
+			}
+		]));
+		assert_eq!(super::diff_pod(&PodState::new(), &a), StateDiff(map![
+			1.into() => AccountDiff{
+				balance: Diff::Born(69.into()),
+				nonce: Diff::Born(0.into()),
+				code: Diff::Born(vec![]),
+				storage: map![],
+			}
+		]));
+	}
+
+	#[test]
+	fn create_delete_with_unchanged() {
+		let a = PodState::from(map![ 1.into() => PodAccount::new(69.into(), 0.into(), vec![], map![]) ]);
+		let b = PodState::from(map![
+			1.into() => PodAccount::new(69.into(), 0.into(), vec![], map![]),
+			2.into() => PodAccount::new(69.into(), 0.into(), vec![], map![])
+		]);
+		assert_eq!(super::diff_pod(&a, &b), StateDiff(map![
+			2.into() => AccountDiff{
+				balance: Diff::Born(69.into()),
+				nonce: Diff::Born(0.into()),
+				code: Diff::Born(vec![]),
+				storage: map![],
+			}
+		]));
+		assert_eq!(super::diff_pod(&b, &a), StateDiff(map![
+			2.into() => AccountDiff{
+				balance: Diff::Died(69.into()),
+				nonce: Diff::Died(0.into()),
+				code: Diff::Died(vec![]),
+				storage: map![],
+			}
+		]));
+	}
+
+	#[test]
+	fn change_with_unchanged() {
+		let a = PodState::from(map![
+			1.into() => PodAccount::new(69.into(), 0.into(), vec![], map![]),
+			2.into() => PodAccount::new(69.into(), 0.into(), vec![], map![])
+		]);
+		let b = PodState::from(map![
+			1.into() => PodAccount::new(69.into(), 1.into(), vec![], map![]),
+			2.into() => PodAccount::new(69.into(), 0.into(), vec![], map![])
+		]);
+		assert_eq!(super::diff_pod(&a, &b), StateDiff(map![
+			1.into() => AccountDiff{
+				balance: Diff::Same,
+				nonce: Diff::Changed(0.into(), 1.into()),
+				code: Diff::Same,
+				storage: map![],
+			}
+		]));
+	}
+
+}
diff --git a/ethcore/src/state.rs b/ethcore/src/state.rs
index 51162bb8e..06a365bdd 100644
--- a/ethcore/src/state.rs
+++ b/ethcore/src/state.rs
@@ -20,13 +20,9 @@ use executive::{Executive, TransactOptions};
 use evm::Factory as EvmFactory;
 use account_db::*;
 use trace::Trace;
-#[cfg(test)]
-#[cfg(feature = "json-tests")]
 use pod_account::*;
-#[cfg(test)]
-#[cfg(feature = "json-tests")]
-use pod_state::PodState;
-//use state_diff::*;	// TODO: uncomment once to_pod() works correctly.
+use pod_state::{self, PodState};
+use types::state_diff::StateDiff;
 
 /// Used to return information about an `State::apply` operation.
 pub struct ApplyOutcome {
@@ -224,7 +220,7 @@ impl State {
 		let e = try!(Executive::new(self, env_info, engine, vm_factory).transact(t, options));
 
 		// TODO uncomment once to_pod() works correctly.
-//		trace!("Applied transaction. Diff:\n{}\n", StateDiff::diff_pod(&old, &self.to_pod()));
+//		trace!("Applied transaction. Diff:\n{}\n", state_diff::diff_pod(&old, &self.to_pod()));
 		self.commit();
 		let receipt = Receipt::new(self.root().clone(), e.cumulative_gas_used, e.logs);
 //		trace!("Transaction receipt: {:?}", receipt);
@@ -275,12 +271,11 @@ impl State {
 		}
 	}
 
-	#[cfg(test)]
-	#[cfg(feature = "json-tests")]
 	/// Populate a PodAccount map from this state.
 	pub fn to_pod(&self) -> PodState {
 		assert!(self.snapshots.borrow().is_empty());
 		// TODO: handle database rather than just the cache.
+		// will need fat db.
 		PodState::from(self.cache.borrow().iter().fold(BTreeMap::new(), |mut m, (add, opt)| {
 			if let Some(ref acc) = *opt {
 				m.insert(add.clone(), PodAccount::from_account(acc));
@@ -289,6 +284,25 @@ impl State {
 		}))
 	}
 
+	fn query_pod(&mut self, query: &PodState) {
+		for (ref address, ref pod_account) in query.get() {
+			if self.get(address, true).is_some() {
+				for (ref key, _) in &pod_account.storage {
+					self.storage_at(address, key);
+				}
+			}
+		}
+	}
+
+	/// Returns a `StateDiff` describing the difference from `orig` to `self`.
+	/// Consumes self.
+	pub fn diff_from(&self, orig: State) -> StateDiff {
+		let pod_state_post = self.to_pod();
+		let mut state_pre = orig;
+		state_pre.query_pod(&pod_state_post);
+		pod_state::diff_pod(&state_pre.to_pod(), &pod_state_post)
+	}
+
 	/// Pull account `a` in our cache from the trie DB and return it.
 	/// `require_code` requires that the code be cached, too.
 	fn get<'a>(&'a self, a: &Address, require_code: bool) -> &'a Option<Account> {
diff --git a/ethcore/src/account_diff.rs b/ethcore/src/types/account_diff.rs
similarity index 68%
rename from ethcore/src/account_diff.rs
rename to ethcore/src/types/account_diff.rs
index c02b7ec7b..49fc51110 100644
--- a/ethcore/src/account_diff.rs
+++ b/ethcore/src/types/account_diff.rs
@@ -17,10 +17,48 @@
 //! Diff between two accounts.
 
 use util::*;
-#[cfg(test)]
-use pod_account::*;
 
-#[derive(Debug,Clone,PartialEq,Eq)]
+#[derive(Debug, PartialEq, Eq, Clone)]
+/// Diff type for specifying a change (or not).
+pub enum Diff<T> where T: Eq {
+	/// Both sides are the same.
+	Same,
+	/// Left (pre, source) side doesn't include value, right side (post, destination) does.
+	Born(T),
+	/// Both sides include data; it chaged value between them.
+	Changed(T, T),
+	/// Left (pre, source) side does include value, right side (post, destination) does not.
+	Died(T),
+}
+
+impl<T> Diff<T> where T: Eq {
+	/// Construct new object with given `pre` and `post`.
+	pub fn new(pre: T, post: T) -> Self { if pre == post { Diff::Same } else { Diff::Changed(pre, post) } }
+
+	/// Get the before value, if there is one.
+	pub fn pre(&self) -> Option<&T> { match *self { Diff::Died(ref x) | Diff::Changed(ref x, _) => Some(x), _ => None } }
+
+	/// Get the after value, if there is one.
+	pub fn post(&self) -> Option<&T> { match *self { Diff::Born(ref x) | Diff::Changed(_, ref x) => Some(x), _ => None } }
+
+	/// Determine whether there was a change or not.
+	pub fn is_same(&self) -> bool { match *self { Diff::Same => true, _ => false }}
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+/// Account diff.
+pub struct AccountDiff {
+	/// Change in balance, allowed to be `Diff::Same`.
+	pub balance: Diff<U256>,
+	/// Change in nonce, allowed to be `Diff::Same`.
+	pub nonce: Diff<U256>,					// Allowed to be Same
+	/// Change in code, allowed to be `Diff::Same`.
+	pub code: Diff<Bytes>,					// Allowed to be Same
+	/// Change in storage, values are not allowed to be `Diff::Same`.
+	pub storage: BTreeMap<H256, Diff<H256>>,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
 /// Change in existance type. 
 // TODO: include other types of change.
 pub enum Existance {
@@ -43,19 +81,6 @@ impl fmt::Display for Existance {
 	}
 }
 
-#[derive(Debug,Clone,PartialEq,Eq)]
-/// Account diff.
-pub struct AccountDiff {
-	/// Change in balance, allowed to be `Diff::Same`.
-	pub balance: Diff<U256>,
-	/// Change in nonce, allowed to be `Diff::Same`.
-	pub nonce: Diff<U256>,					// Allowed to be Same
-	/// Change in code, allowed to be `Diff::Same`.
-	pub code: Diff<Bytes>,					// Allowed to be Same
-	/// Change in storage, values are not allowed to be `Diff::Same`.
-	pub storage: BTreeMap<H256, Diff<H256>>,
-}
-
 impl AccountDiff {
 	/// Get `Existance` projection.
 	pub fn existance(&self) -> Existance {
@@ -65,47 +90,6 @@ impl AccountDiff {
 			_ => Existance::Alive,
 		}
 	}
-
-	#[cfg(test)]
-	/// Determine difference between two optionally existant `Account`s. Returns None
-	/// if they are the same.
-	pub fn diff_pod(pre: Option<&PodAccount>, post: Option<&PodAccount>) -> Option<AccountDiff> {
-		match (pre, post) {
-			(None, Some(x)) => Some(AccountDiff {
-				balance: Diff::Born(x.balance),
-				nonce: Diff::Born(x.nonce),
-				code: Diff::Born(x.code.clone()),
-				storage: x.storage.iter().map(|(k, v)| (k.clone(), Diff::Born(v.clone()))).collect(),
-			}),
-			(Some(x), None) => Some(AccountDiff {
-				balance: Diff::Died(x.balance),
-				nonce: Diff::Died(x.nonce),
-				code: Diff::Died(x.code.clone()),
-				storage: x.storage.iter().map(|(k, v)| (k.clone(), Diff::Died(v.clone()))).collect(),
-			}),
-			(Some(pre), Some(post)) => {
-				let storage: Vec<_> = pre.storage.keys().merge(post.storage.keys())
-					.filter(|k| pre.storage.get(k).unwrap_or(&H256::new()) != post.storage.get(k).unwrap_or(&H256::new()))
-					.collect();
-				let r = AccountDiff {
-					balance: Diff::new(pre.balance, post.balance),
-					nonce: Diff::new(pre.nonce, post.nonce),
-					code: Diff::new(pre.code.clone(), post.code.clone()),
-					storage: storage.into_iter().map(|k|
-						(k.clone(), Diff::new(
-							pre.storage.get(&k).cloned().unwrap_or_else(H256::new),
-							post.storage.get(&k).cloned().unwrap_or_else(H256::new)
-						))).collect(),
-				};
-				if r.balance.is_same() && r.nonce.is_same() && r.code.is_same() && r.storage.is_empty() {
-					None
-				} else {
-					Some(r)
-				}
-			},
-			_ => None,
-		}
-	}
 }
 
 // TODO: refactor into something nicer.
diff --git a/ethcore/src/types/executed.rs b/ethcore/src/types/executed.rs
index 823c9dda1..4d31b9fe5 100644
--- a/ethcore/src/types/executed.rs
+++ b/ethcore/src/types/executed.rs
@@ -20,13 +20,14 @@ use util::numbers::*;
 use util::Bytes;
 use trace::{Trace, VMTrace};
 use types::log_entry::LogEntry;
+use types::state_diff::StateDiff;
 use ipc::binary::BinaryConvertError;
 use std::fmt;
 use std::mem;
 use std::collections::VecDeque;
 
 /// Transaction execution receipt.
-#[derive(Debug, PartialEq, Clone, Binary)]
+#[derive(Debug, PartialEq, Clone)]
 pub struct Executed {
 	/// Gas paid up front for execution of transaction.
 	pub gas: U256,
@@ -61,6 +62,8 @@ pub struct Executed {
 	pub trace: Option<Trace>,
 	/// The VM trace of this transaction.
 	pub vm_trace: Option<VMTrace>,
+	/// The state diff, if we traced it.
+	pub state_diff: Option<StateDiff>,
 }
 
 /// Result of executing the transaction.
diff --git a/ethcore/src/types/mod.rs.in b/ethcore/src/types/mod.rs.in
index 1f67a9184..b51e9e57b 100644
--- a/ethcore/src/types/mod.rs.in
+++ b/ethcore/src/types/mod.rs.in
@@ -23,3 +23,5 @@ pub mod log_entry;
 pub mod trace_types;
 pub mod executed;
 pub mod block_status;
+pub mod account_diff;
+pub mod state_diff;
diff --git a/ethcore/src/types/state_diff.rs b/ethcore/src/types/state_diff.rs
new file mode 100644
index 000000000..4257d5b07
--- /dev/null
+++ b/ethcore/src/types/state_diff.rs
@@ -0,0 +1,49 @@
+// Copyright 2015, 2016 Ethcore (UK) Ltd.
+// This file is part of Parity.
+
+// Parity is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity.  If not, see <http://www.gnu.org/licenses/>.
+
+//! State diff module.
+
+use util::*;
+use account_diff::*;
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+/// Expression for the delta between two system states. Encoded the
+/// delta of every altered account.
+pub struct StateDiff (pub BTreeMap<Address, AccountDiff>);
+
+impl StateDiff {
+	/// Get the actual data.
+	pub fn get(&self) -> &BTreeMap<Address, AccountDiff> {
+		&self.0
+	}
+}
+
+impl fmt::Display for StateDiff {
+	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+		for (add, acc) in &self.0 {
+			try!(write!(f, "{} {}: {}", acc.existance(), add, acc));
+		}
+		Ok(())
+	}
+}
+
+impl Deref for StateDiff {
+	type Target = BTreeMap<Address, AccountDiff>;
+
+	fn deref(&self) -> &Self::Target {
+		&self.0
+	}
+}
diff --git a/rpc/src/v1/impls/eth.rs b/rpc/src/v1/impls/eth.rs
index ec98d341e..b0d6abcf0 100644
--- a/rpc/src/v1/impls/eth.rs
+++ b/rpc/src/v1/impls/eth.rs
@@ -511,8 +511,8 @@ impl<C, S, A, M, EM> Eth for EthClient<C, S, A, M, EM> where
 			.and_then(|(request, block_number,)| {
 				let signed = try!(self.sign_call(request));
 				let r = match block_number {
-					BlockNumber::Pending => take_weak!(self.miner).call(take_weak!(self.client).deref(), &signed, false),
-					BlockNumber::Latest => take_weak!(self.client).call(&signed, false),
+					BlockNumber::Pending => take_weak!(self.miner).call(take_weak!(self.client).deref(), &signed, Default::default()),
+					BlockNumber::Latest => take_weak!(self.client).call(&signed, Default::default()),
 					_ => panic!("{:?}", block_number),
 				};
 				to_value(&r.map(|e| Bytes(e.output)).unwrap_or(Bytes::new(vec![])))
@@ -524,8 +524,8 @@ impl<C, S, A, M, EM> Eth for EthClient<C, S, A, M, EM> where
 			.and_then(|(request, block_number,)| {
 				let signed = try!(self.sign_call(request));
 				let r = match block_number {
-					BlockNumber::Pending => take_weak!(self.miner).call(take_weak!(self.client).deref(), &signed, false),
-					BlockNumber::Latest => take_weak!(self.client).call(&signed, false),
+					BlockNumber::Pending => take_weak!(self.miner).call(take_weak!(self.client).deref(), &signed, Default::default()),
+					BlockNumber::Latest => take_weak!(self.client).call(&signed, Default::default()),
 					_ => return Err(Error::invalid_params()),
 				};
 				to_value(&r.map(|res| res.gas_used + res.refunded).unwrap_or(From::from(0)))
diff --git a/rpc/src/v1/impls/ethcore.rs b/rpc/src/v1/impls/ethcore.rs
index ca14ca021..69d036500 100644
--- a/rpc/src/v1/impls/ethcore.rs
+++ b/rpc/src/v1/impls/ethcore.rs
@@ -22,9 +22,12 @@ use std::sync::{Arc, Weak};
 use std::ops::Deref;
 use std::collections::BTreeMap;
 use jsonrpc_core::*;
+use serde;
 use ethcore::miner::MinerService;
+use ethcore::state_diff::StateDiff;
+use ethcore::account_diff::{Diff, Existance};
 use ethcore::transaction::{Transaction as EthTransaction, SignedTransaction, Action};
-use ethcore::client::BlockChainClient;
+use ethcore::client::{BlockChainClient, CallAnalytics};
 use ethcore::trace::VMTrace;
 use v1::traits::Ethcore;
 use v1::types::{Bytes, CallRequest};
@@ -115,6 +118,47 @@ fn vm_trace_to_object(t: &VMTrace) -> Value {
 	Value::Object(ret)
 }
 
+fn diff_to_object<T>(d: &Diff<T>) -> Value where T: serde::Serialize + Eq {
+	let mut ret = BTreeMap::new();
+	match *d {
+		Diff::Same => {
+			ret.insert("diff".to_owned(), Value::String("=".to_owned()));
+		}
+		Diff::Born(ref x) => {
+			ret.insert("diff".to_owned(), Value::String("+".to_owned()));
+			ret.insert("+".to_owned(), to_value(x).unwrap());
+		}
+		Diff::Died(ref x) => {
+			ret.insert("diff".to_owned(), Value::String("-".to_owned()));
+			ret.insert("-".to_owned(), to_value(x).unwrap());
+		}
+		Diff::Changed(ref from, ref to) => {
+			ret.insert("diff".to_owned(), Value::String("*".to_owned()));
+			ret.insert("-".to_owned(), to_value(from).unwrap());
+			ret.insert("+".to_owned(), to_value(to).unwrap());
+		}
+	};
+	Value::Object(ret)
+}
+
+fn state_diff_to_object(t: &StateDiff) -> Value {
+	Value::Object(t.iter().map(|(address, account)| {
+		(address.hex(), Value::Object(map![
+			"existance".to_owned() => Value::String(match account.existance() {
+				Existance::Born => "+",
+				Existance::Alive => ".",
+				Existance::Died => "-",
+			}.to_owned()),
+			"balance".to_owned() => diff_to_object(&account.balance),
+			"nonce".to_owned() => diff_to_object(&account.nonce),
+			"code".to_owned() => diff_to_object(&account.code),
+			"storage".to_owned() => Value::Object(account.storage.iter().map(|(key, val)| {
+				(key.hex(), diff_to_object(&val))
+			}).collect::<BTreeMap<_, _>>())
+		]))
+	}).collect::<BTreeMap<_, _>>())
+}
+
 impl<C, M> Ethcore for EthcoreClient<C, M> where C: BlockChainClient + 'static, M: MinerService + 'static {
 
 	fn set_min_gas_price(&self, params: Params) -> Result<Value, Error> {
@@ -211,7 +255,7 @@ impl<C, M> Ethcore for EthcoreClient<C, M> where C: BlockChainClient + 'static,
 		from_params(params)
 			.and_then(|(request,)| {
 				let signed = try!(self.sign_call(request));
-				let r = take_weak!(self.client).call(&signed, true);
+				let r = take_weak!(self.client).call(&signed, CallAnalytics{ vm_tracing: true, state_diffing: false });
 				if let Ok(executed) = r {
 					if let Some(vm_trace) = executed.vm_trace {
 						return Ok(vm_trace_to_object(&vm_trace));
@@ -220,4 +264,19 @@ impl<C, M> Ethcore for EthcoreClient<C, M> where C: BlockChainClient + 'static,
 				Ok(Value::Null)
 			})
 	}
+
+	fn state_diff_call(&self, params: Params) -> Result<Value, Error> {
+		trace!(target: "jsonrpc", "state_diff_call: {:?}", params);
+		from_params(params)
+			.and_then(|(request,)| {
+				let signed = try!(self.sign_call(request));
+				let r = take_weak!(self.client).call(&signed, CallAnalytics{ vm_tracing: false, state_diffing: true });
+				if let Ok(executed) = r {
+					if let Some(state_diff) = executed.state_diff {
+						return Ok(state_diff_to_object(&state_diff));
+					}
+				}
+				Ok(Value::Null)
+			})
+	}
 }
diff --git a/rpc/src/v1/tests/helpers/miner_service.rs b/rpc/src/v1/tests/helpers/miner_service.rs
index 0f9327887..daa5c9497 100644
--- a/rpc/src/v1/tests/helpers/miner_service.rs
+++ b/rpc/src/v1/tests/helpers/miner_service.rs
@@ -19,7 +19,7 @@
 use util::{Address, H256, Bytes, U256, FixedHash, Uint};
 use util::standard::*;
 use ethcore::error::{Error, ExecutionError};
-use ethcore::client::{MiningBlockChainClient, Executed};
+use ethcore::client::{MiningBlockChainClient, Executed, CallAnalytics};
 use ethcore::block::{ClosedBlock, IsBlock};
 use ethcore::transaction::SignedTransaction;
 use ethcore::receipt::Receipt;
@@ -202,7 +202,7 @@ impl MinerService for TestMinerService {
 		self.latest_closed_block.lock().unwrap().as_ref().map_or_else(U256::zero, |b| b.block().fields().state.balance(address).clone())
 	}
 
-	fn call(&self, _chain: &MiningBlockChainClient, _t: &SignedTransaction, _vm_tracing: bool) -> Result<Executed, ExecutionError> {
+	fn call(&self, _chain: &MiningBlockChainClient, _t: &SignedTransaction, _analytics: CallAnalytics) -> Result<Executed, ExecutionError> {
 		unimplemented!();
 	}
 
diff --git a/rpc/src/v1/tests/mocked/eth.rs b/rpc/src/v1/tests/mocked/eth.rs
index 4f43be827..34708e232 100644
--- a/rpc/src/v1/tests/mocked/eth.rs
+++ b/rpc/src/v1/tests/mocked/eth.rs
@@ -431,6 +431,7 @@ fn rpc_eth_call() {
 		output: vec![0x12, 0x34, 0xff],
 		trace: None,
 		vm_trace: None,
+		state_diff: None,
 	});
 
 	let request = r#"{
@@ -465,6 +466,7 @@ fn rpc_eth_call_default_block() {
 		output: vec![0x12, 0x34, 0xff],
 		trace: None,
 		vm_trace: None,
+		state_diff: None,
 	});
 
 	let request = r#"{
@@ -498,6 +500,7 @@ fn rpc_eth_estimate_gas() {
 		output: vec![0x12, 0x34, 0xff],
 		trace: None,
 		vm_trace: None,
+		state_diff: None,
 	});
 
 	let request = r#"{
@@ -532,6 +535,7 @@ fn rpc_eth_estimate_gas_default_block() {
 		output: vec![0x12, 0x34, 0xff],
 		trace: None,
 		vm_trace: None,
+		state_diff: None,
 	});
 
 	let request = r#"{
diff --git a/rpc/src/v1/traits/ethcore.rs b/rpc/src/v1/traits/ethcore.rs
index abc87bbb8..116a4cd05 100644
--- a/rpc/src/v1/traits/ethcore.rs
+++ b/rpc/src/v1/traits/ethcore.rs
@@ -75,6 +75,9 @@ pub trait Ethcore: Sized + Send + Sync + 'static {
 	/// Executes the given call and returns the VM trace for it.
 	fn vm_trace_call(&self, _: Params) -> Result<Value, Error>;
 
+	/// Executes the given call and returns the diff for it.
+	fn state_diff_call(&self, params: Params) -> Result<Value, Error>;
+
 	/// Should be used to convert object to io delegate.
 	fn to_delegate(self) -> IoDelegate<Self> {
 		let mut delegate = IoDelegate::new(Arc::new(self));
@@ -98,6 +101,7 @@ pub trait Ethcore: Sized + Send + Sync + 'static {
 		delegate.add_method("ethcore_defaultExtraData", Ethcore::default_extra_data);
 
 		delegate.add_method("ethcore_vmTraceCall", Ethcore::vm_trace_call);
+		delegate.add_method("ethcore_stateDiffCall", Ethcore::state_diff_call);
 
 		delegate
 	}
diff --git a/util/src/misc.rs b/util/src/misc.rs
index 159381603..8d22e04d7 100644
--- a/util/src/misc.rs
+++ b/util/src/misc.rs
@@ -24,33 +24,6 @@ use target_info::Target;
 include!(concat!(env!("OUT_DIR"), "/version.rs"));
 include!(concat!(env!("OUT_DIR"), "/rustc_version.rs"));
 
-#[derive(Debug,Clone,PartialEq,Eq)]
-/// Diff type for specifying a change (or not).
-pub enum Diff<T> where T: Eq {
-	/// Both sides are the same.
-	Same,
-	/// Left (pre, source) side doesn't include value, right side (post, destination) does.
-	Born(T),
-	/// Both sides include data; it chaged value between them.
-	Changed(T, T),
-	/// Left (pre, source) side does include value, right side (post, destination) does not.
-	Died(T),
-}
-
-impl<T> Diff<T> where T: Eq {
-	/// Construct new object with given `pre` and `post`.
-	pub fn new(pre: T, post: T) -> Self { if pre == post { Diff::Same } else { Diff::Changed(pre, post) } }
-
-	/// Get the before value, if there is one.
-	pub fn pre(&self) -> Option<&T> { match *self { Diff::Died(ref x) | Diff::Changed(ref x, _) => Some(x), _ => None } }
-
-	/// Get the after value, if there is one.
-	pub fn post(&self) -> Option<&T> { match *self { Diff::Born(ref x) | Diff::Changed(_, ref x) => Some(x), _ => None } }
-
-	/// Determine whether there was a change or not.
-	pub fn is_same(&self) -> bool { match *self { Diff::Same => true, _ => false }}
-}
-
 #[derive(PartialEq,Eq,Clone,Copy)]
 /// Boolean type for clean/dirty status.
 pub enum Filth {