diff --git a/ethcore/src/client/evm_test_client.rs b/ethcore/src/client/evm_test_client.rs
index 1cc68596b..945de14d7 100644
--- a/ethcore/src/client/evm_test_client.rs
+++ b/ethcore/src/client/evm_test_client.rs
@@ -104,7 +104,7 @@ impl EvmTestClient {
 		let mut tracer = trace::NoopTracer;
 		let mut output = vec![];
 		let mut executive = executive::Executive::new(&mut state, &info, &*self.spec.engine);
-		let gas_left = executive.call(
+		let (gas_left, _) = executive.call(
 			params,
 			&mut substate,
 			util::BytesRef::Flexible(&mut output),
diff --git a/ethcore/src/evm/evm.rs b/ethcore/src/evm/evm.rs
index 523f98d18..46457c35f 100644
--- a/ethcore/src/evm/evm.rs
+++ b/ethcore/src/evm/evm.rs
@@ -97,10 +97,45 @@ impl fmt::Display for Error {
 /// A specialized version of Result over EVM errors.
 pub type Result<T> = ::std::result::Result<T, Error>;
 
+
+/// Return data buffer. Holds memory from a previous call and a slice into that memory.
+#[derive(Debug)]
+pub struct ReturnData {
+	mem: Vec<u8>,
+	offset: usize,
+	size: usize,
+}
+
+impl ::std::ops::Deref for ReturnData {
+	type Target = [u8];
+	fn deref(&self) -> &[u8] {
+		&self.mem[self.offset..self.offset + self.size]
+	}
+}
+
+impl ReturnData {
+	/// Create empty `ReturnData`.
+	pub fn empty() -> Self {
+		ReturnData {
+			mem: Vec::new(),
+			offset: 0,
+			size: 0,
+		}
+	}
+	/// Create `ReturnData` from give buffer and slice.
+	pub fn new(mem: Vec<u8>, offset: usize, size: usize) -> Self {
+		ReturnData {
+			mem: mem,
+			offset: offset,
+			size: size,
+		}
+	}
+}
+
 /// Gas Left: either it is a known value, or it needs to be computed by processing
 /// a return instruction.
-#[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
-pub enum GasLeft<'a> {
+#[derive(Debug)]
+pub enum GasLeft {
 	/// Known gas left
 	Known(U256),
 	/// Return or Revert instruction must be processed.
@@ -108,7 +143,7 @@ pub enum GasLeft<'a> {
 		/// Amount of gas left.
 		gas_left: U256,
 		/// Return data buffer.
-		data: &'a [u8],
+		data: ReturnData,
 		/// Apply or revert state changes on revert.
 		apply_state: bool
 	},
@@ -122,6 +157,8 @@ pub struct FinalizationResult {
 	pub gas_left: U256,
 	/// Apply execution state changes or revert them.
 	pub apply_state: bool,
+	/// Return data buffer.
+	pub return_data: ReturnData,
 }
 
 /// Types that can be "finalized" using an EVM.
@@ -133,13 +170,14 @@ pub trait Finalize {
 	fn finalize<E: Ext>(self, ext: E) -> Result<FinalizationResult>;
 }
 
-impl<'a> Finalize for Result<GasLeft<'a>> {
+impl Finalize for Result<GasLeft> {
 	fn finalize<E: Ext>(self, ext: E) -> Result<FinalizationResult> {
 		match self {
-			Ok(GasLeft::Known(gas_left)) => Ok(FinalizationResult { gas_left: gas_left, apply_state: true }),
-			Ok(GasLeft::NeedsReturn {gas_left, data, apply_state}) => ext.ret(&gas_left, data).map(|gas_left| FinalizationResult {
+			Ok(GasLeft::Known(gas_left)) => Ok(FinalizationResult { gas_left: gas_left, apply_state: true, return_data: ReturnData::empty() }),
+			Ok(GasLeft::NeedsReturn {gas_left, data, apply_state}) => ext.ret(&gas_left, &data).map(|gas_left| FinalizationResult {
 				gas_left: gas_left,
 				apply_state: apply_state,
+				return_data: data,
 			}),
 			Err(err) => Err(err),
 		}
diff --git a/ethcore/src/evm/ext.rs b/ethcore/src/evm/ext.rs
index fbdc3cec4..cc294dbd4 100644
--- a/ethcore/src/evm/ext.rs
+++ b/ethcore/src/evm/ext.rs
@@ -17,7 +17,7 @@
 //! Interface for Evm externalities.
 
 use util::*;
-use evm::{self, Schedule};
+use evm::{self, Schedule, ReturnData};
 use env_info::*;
 use types::executed::CallType;
 
@@ -34,8 +34,8 @@ pub enum ContractCreateResult {
 /// Result of externalities call function.
 pub enum MessageCallResult {
 	/// Returned when message call was successfull.
-	/// Contains gas left.
-	Success(U256),
+	/// Contains gas left and output data.
+	Success(U256, ReturnData),
 	/// Returned when message call failed.
 	/// VM doesn't have to know the reason.
 	Failed
@@ -109,7 +109,7 @@ pub trait Ext {
 
 	/// Should be called when transaction calls `RETURN` opcode.
 	/// Returns gas_left if cost of returning the data is not too high.
-	fn ret(self, gas: &U256, data: &[u8]) -> evm::Result<U256> where Self: Sized;
+	fn ret(self, gas: &U256, data: &ReturnData) -> evm::Result<U256>;
 
 	/// Should be called when contract commits suicide.
 	/// Address to which funds should be refunded.
diff --git a/ethcore/src/evm/instructions.rs b/ethcore/src/evm/instructions.rs
index 2fb6cfd66..f726c9166 100644
--- a/ethcore/src/evm/instructions.rs
+++ b/ethcore/src/evm/instructions.rs
@@ -178,6 +178,8 @@ lazy_static! {
 		arr[ADDMOD as usize] =			InstructionInfo::new("ADDMOD",			0, 3, 1, false, GasPriceTier::Mid);
 		arr[MULMOD as usize] =			InstructionInfo::new("MULMOD",			0, 3, 1, false, GasPriceTier::Mid);
 		arr[SIGNEXTEND as usize] =		InstructionInfo::new("SIGNEXTEND",		0, 2, 1, false, GasPriceTier::Low);
+		arr[RETURNDATASIZE as usize] =	InstructionInfo::new("RETURNDATASIZE",	0, 0, 1, false, GasPriceTier::Base);
+		arr[RETURNDATACOPY as usize] =	InstructionInfo::new("RETURNDATACOPY",	0, 3, 0, true, GasPriceTier::VeryLow);
 		arr[SHA3 as usize] =			InstructionInfo::new("SHA3",			0, 2, 1, false, GasPriceTier::Special);
 		arr[ADDRESS as usize] = 		InstructionInfo::new("ADDRESS",			0, 0, 1, false, GasPriceTier::Base);
 		arr[BALANCE as usize] = 		InstructionInfo::new("BALANCE",			0, 1, 1, false, GasPriceTier::Special);
@@ -369,6 +371,10 @@ pub const GASPRICE: Instruction = 0x3a;
 pub const EXTCODESIZE: Instruction = 0x3b;
 /// copy external code (from another contract)
 pub const EXTCODECOPY: Instruction = 0x3c;
+/// get the size of the return data buffer for the last call
+pub const RETURNDATASIZE: Instruction = 0x3d;
+/// copy return data buffer to memory
+pub const RETURNDATACOPY: Instruction = 0x3e;
 
 /// get hash of most recent complete block
 pub const BLOCKHASH: Instruction = 0x40;
diff --git a/ethcore/src/evm/interpreter/gasometer.rs b/ethcore/src/evm/interpreter/gasometer.rs
index 4d8350e91..e76a5971e 100644
--- a/ethcore/src/evm/interpreter/gasometer.rs
+++ b/ethcore/src/evm/interpreter/gasometer.rs
@@ -173,7 +173,7 @@ impl<Gas: CostType> Gasometer<Gas> {
 				let gas = Gas::from(schedule.sha3_gas) + (Gas::from(schedule.sha3_word_gas) * words);
 				Request::GasMem(gas, mem_needed(stack.peek(0), stack.peek(1))?)
 			},
-			instructions::CALLDATACOPY | instructions::CODECOPY => {
+			instructions::CALLDATACOPY | instructions::CODECOPY | instructions::RETURNDATACOPY => {
 				Request::GasMemCopy(default_gas, mem_needed(stack.peek(0), stack.peek(2))?, Gas::from_u256(*stack.peek(2))?)
 			},
 			instructions::EXTCODECOPY => {
diff --git a/ethcore/src/evm/interpreter/memory.rs b/ethcore/src/evm/interpreter/memory.rs
index 39c0d8025..555e4bc30 100644
--- a/ethcore/src/evm/interpreter/memory.rs
+++ b/ethcore/src/evm/interpreter/memory.rs
@@ -15,6 +15,9 @@
 // along with Parity.  If not, see <http://www.gnu.org/licenses/>.
 
 use util::U256;
+use evm::ReturnData;
+
+const MAX_RETURN_WASTE_BYTES: usize = 16384;
 
 pub trait Memory {
 	/// Retrieve current size of the memory
@@ -36,6 +39,8 @@ pub trait Memory {
 	/// Retrieve writeable part of memory
 	fn writeable_slice(&mut self, offset: U256, size: U256) -> &mut[u8];
 	fn dump(&self);
+	/// Convert memory into return data.
+	fn into_return_data(self, offset: U256, size: U256) -> ReturnData;
 }
 
 /// Checks whether offset and size is valid memory range
@@ -109,6 +114,21 @@ impl Memory for Vec<u8> {
 			Memory::resize(self, size)
 		}
 	}
+
+	fn into_return_data(mut self, offset: U256, size: U256) -> ReturnData {
+		let mut offset = offset.low_u64() as usize;
+		let size = size.low_u64() as usize;
+		if !is_valid_range(offset, size) {
+			return ReturnData::empty()
+		}
+		if self.len() - size > MAX_RETURN_WASTE_BYTES {
+			{ let _ =  self.drain(..offset); }
+			self.truncate(size);
+			self.shrink_to_fit();
+			offset = 0;
+		}
+		ReturnData::new(self, offset, size)
+	}
 }
 
 #[cfg(test)]
@@ -164,4 +184,4 @@ mod tests {
 			assert_eq!(mem.read_slice(U256::from(0), U256::from(7)), "a67890g".as_bytes());
 		}
 	}
-}
\ No newline at end of file
+}
diff --git a/ethcore/src/evm/interpreter/mod.rs b/ethcore/src/evm/interpreter/mod.rs
index fe3f34013..8b8b739e0 100644
--- a/ethcore/src/evm/interpreter/mod.rs
+++ b/ethcore/src/evm/interpreter/mod.rs
@@ -32,7 +32,7 @@ use std::marker::PhantomData;
 use action_params::{ActionParams, ActionValue};
 use types::executed::CallType;
 use evm::instructions::{self, Instruction, InstructionInfo};
-use evm::{self, MessageCallResult, ContractCreateResult, GasLeft, CostType, CreateContractAddress};
+use evm::{self, MessageCallResult, ContractCreateResult, GasLeft, CostType, CreateContractAddress, ReturnData};
 use bit_set::BitSet;
 
 use util::*;
@@ -102,6 +102,7 @@ enum InstructionResult<Gas> {
 pub struct Interpreter<Cost: CostType> {
 	mem: Vec<u8>,
 	cache: Arc<SharedCache>,
+	return_data: ReturnData,
 	_type: PhantomData<Cost>,
 }
 
@@ -166,9 +167,10 @@ impl<Cost: CostType> evm::Evm for Interpreter<Cost> {
 				},
 				InstructionResult::StopExecutionNeedsReturn {gas, init_off, init_size, apply} => {
 					informant.done();
+					let mem = mem::replace(&mut self.mem, Vec::new());
 					return Ok(GasLeft::NeedsReturn {
 						gas_left: gas.as_u256(),
-						data: self.mem.read_slice(init_off, init_size),
+						data: mem.into_return_data(init_off, init_size),
 						apply_state: apply
 					});
 				},
@@ -187,6 +189,7 @@ impl<Cost: CostType> Interpreter<Cost> {
 		Interpreter {
 			mem: Vec::new(),
 			cache: cache,
+			return_data: ReturnData::empty(),
 			_type: PhantomData::default(),
 		}
 	}
@@ -233,7 +236,7 @@ impl<Cost: CostType> Interpreter<Cost> {
 		match instruction {
 			instructions::MSTORE | instructions::MLOAD => Some((stack.peek(0).low_u64() as usize, 32)),
 			instructions::MSTORE8 => Some((stack.peek(0).low_u64() as usize, 1)),
-			instructions::CALLDATACOPY | instructions::CODECOPY => Some((stack.peek(0).low_u64() as usize, stack.peek(2).low_u64() as usize)),
+			instructions::CALLDATACOPY | instructions::CODECOPY | instructions::RETURNDATACOPY => Some((stack.peek(0).low_u64() as usize, stack.peek(2).low_u64() as usize)),
 			instructions::EXTCODECOPY => Some((stack.peek(1).low_u64() as usize, stack.peek(3).low_u64() as usize)),
 			instructions::CALL | instructions::CALLCODE => Some((stack.peek(5).low_u64() as usize, stack.peek(6).low_u64() as usize)),
 			instructions::DELEGATECALL => Some((stack.peek(4).low_u64() as usize, stack.peek(5).low_u64() as usize)),
@@ -362,8 +365,9 @@ impl<Cost: CostType> Interpreter<Cost> {
 				};
 
 				return match call_result {
-					MessageCallResult::Success(gas_left) => {
+					MessageCallResult::Success(gas_left, data) => {
 						stack.push(U256::one());
+						self.return_data = data;
 						Ok(InstructionResult::UnusedGas(Cost::from_u256(gas_left).expect("Gas left cannot be greater then current one")))
 					},
 					MessageCallResult::Failed  => {
@@ -495,21 +499,27 @@ impl<Cost: CostType> Interpreter<Cost> {
 			instructions::CODESIZE => {
 				stack.push(U256::from(code.len()));
 			},
+			instructions::RETURNDATASIZE => {
+				stack.push(U256::from(self.return_data.len()))
+			},
 			instructions::EXTCODESIZE => {
 				let address = u256_to_address(&stack.pop_back());
 				let len = ext.extcodesize(&address)?;
 				stack.push(U256::from(len));
 			},
 			instructions::CALLDATACOPY => {
-				self.copy_data_to_memory(stack, params.data.as_ref().map_or_else(|| &[] as &[u8], |d| &*d as &[u8]));
+				Self::copy_data_to_memory(&mut self.mem, stack, params.data.as_ref().map_or_else(|| &[] as &[u8], |d| &*d as &[u8]));
+			},
+			instructions::RETURNDATACOPY => {
+				Self::copy_data_to_memory(&mut self.mem, stack, &*self.return_data);
 			},
 			instructions::CODECOPY => {
-				self.copy_data_to_memory(stack, params.code.as_ref().map_or_else(|| &[] as &[u8], |c| &**c as &[u8]));
+				Self::copy_data_to_memory(&mut self.mem, stack, params.code.as_ref().map_or_else(|| &[] as &[u8], |c| &**c as &[u8]));
 			},
 			instructions::EXTCODECOPY => {
 				let address = u256_to_address(&stack.pop_back());
 				let code = ext.extcode(&address)?;
-				self.copy_data_to_memory(stack, &code);
+				Self::copy_data_to_memory(&mut self.mem, stack, &code);
 			},
 			instructions::GASPRICE => {
 				stack.push(params.gas_price.clone());
@@ -541,7 +551,7 @@ impl<Cost: CostType> Interpreter<Cost> {
 		Ok(InstructionResult::Ok)
 	}
 
-	fn copy_data_to_memory(&mut self, stack: &mut Stack<U256>, source: &[u8]) {
+	fn copy_data_to_memory(mem: &mut Vec<u8>, stack: &mut Stack<U256>, source: &[u8]) {
 		let dest_offset = stack.pop_back();
 		let source_offset = stack.pop_back();
 		let size = stack.pop_back();
@@ -550,9 +560,9 @@ impl<Cost: CostType> Interpreter<Cost> {
 		let output_end = match source_offset > source_size || size > source_size || source_offset + size > source_size {
 			true => {
 				let zero_slice = if source_offset > source_size {
-					self.mem.writeable_slice(dest_offset, size)
+					mem.writeable_slice(dest_offset, size)
 				} else {
-					self.mem.writeable_slice(dest_offset + source_size - source_offset, source_offset + size - source_size)
+					mem.writeable_slice(dest_offset + source_size - source_offset, source_offset + size - source_size)
 				};
 				for i in zero_slice.iter_mut() {
 					*i = 0;
@@ -564,7 +574,7 @@ impl<Cost: CostType> Interpreter<Cost> {
 
 		if source_offset < source_size {
 			let output_begin = source_offset.low_u64() as usize;
-			self.mem.write_slice(dest_offset, &source[output_begin..output_end]);
+			mem.write_slice(dest_offset, &source[output_begin..output_end]);
 		}
 	}
 
diff --git a/ethcore/src/evm/mod.rs b/ethcore/src/evm/mod.rs
index 3b27c1f31..1ac05ce61 100644
--- a/ethcore/src/evm/mod.rs
+++ b/ethcore/src/evm/mod.rs
@@ -33,7 +33,7 @@ mod tests;
 #[cfg(all(feature="benches", test))]
 mod benches;
 
-pub use self::evm::{Evm, Error, Finalize, FinalizationResult, GasLeft, Result, CostType};
+pub use self::evm::{Evm, Error, Finalize, FinalizationResult, GasLeft, Result, CostType, ReturnData};
 pub use self::ext::{Ext, ContractCreateResult, MessageCallResult, CreateContractAddress};
 pub use self::vmtype::VMType;
 pub use self::factory::Factory;
diff --git a/ethcore/src/evm/tests.rs b/ethcore/src/evm/tests.rs
index b6e783c91..462a632b4 100644
--- a/ethcore/src/evm/tests.rs
+++ b/ethcore/src/evm/tests.rs
@@ -18,7 +18,7 @@ use util::*;
 use action_params::{ActionParams, ActionValue};
 use env_info::EnvInfo;
 use types::executed::CallType;
-use evm::{self, Ext, Schedule, Factory, GasLeft, VMType, ContractCreateResult, MessageCallResult, CreateContractAddress};
+use evm::{self, Ext, Schedule, Factory, GasLeft, VMType, ContractCreateResult, MessageCallResult, CreateContractAddress, ReturnData};
 use std::fmt::Debug;
 use tests::helpers::*;
 use types::transaction::SYSTEM_ADDRESS;
@@ -149,7 +149,7 @@ impl Ext for FakeExt {
 			data: data.to_vec(),
 			code_address: Some(code_address.clone())
 		});
-		MessageCallResult::Success(*gas)
+		MessageCallResult::Success(*gas, ReturnData::empty())
 	}
 
 	fn extcode(&self, address: &Address) -> trie::Result<Arc<Bytes>> {
@@ -167,7 +167,7 @@ impl Ext for FakeExt {
 		});
 	}
 
-	fn ret(self, _gas: &U256, _data: &[u8]) -> evm::Result<U256> {
+	fn ret(self, _gas: &U256, _data: &ReturnData) -> evm::Result<U256> {
 		unimplemented!();
 	}
 
diff --git a/ethcore/src/executive.rs b/ethcore/src/executive.rs
index 36efdd2e7..b5b5fb959 100644
--- a/ethcore/src/executive.rs
+++ b/ethcore/src/executive.rs
@@ -22,7 +22,7 @@ use engines::Engine;
 use types::executed::CallType;
 use env_info::EnvInfo;
 use error::ExecutionError;
-use evm::{self, Ext, Finalize, CreateContractAddress, FinalizationResult};
+use evm::{self, Ext, Finalize, CreateContractAddress, FinalizationResult, ReturnData};
 use externalities::*;
 use trace::{FlatTrace, Tracer, NoopTracer, ExecutiveTracer, VMTrace, VMTracer, ExecutiveVMTracer, NoopVMTracer};
 use transaction::{Action, SignedTransaction};
@@ -194,7 +194,7 @@ impl<'a, B: 'a + StateBackend, E: Engine + ?Sized> Executive<'a, B, E> {
 
 		let mut substate = Substate::new();
 
-		let (gas_left, output) = match t.action {
+		let (result, output) = match t.action {
 			Action::Create => {
 				let code_hash = t.data.sha3();
 				let new_address = contract_address(self.engine.create_address_scheme(self.info.number), &sender, &nonce, &code_hash);
@@ -233,7 +233,7 @@ impl<'a, B: 'a + StateBackend, E: Engine + ?Sized> Executive<'a, B, E> {
 		};
 
 		// finalize here!
-		Ok(self.finalize(t, substate, gas_left, output, tracer.traces(), vm_tracer.drain())?)
+		Ok(self.finalize(t, substate, result, output, tracer.traces(), vm_tracer.drain())?)
 	}
 
 	fn exec_vm<T, V>(
@@ -279,7 +279,7 @@ impl<'a, B: 'a + StateBackend, E: Engine + ?Sized> Executive<'a, B, E> {
 		mut output: BytesRef,
 		tracer: &mut T,
 		vm_tracer: &mut V
-	) -> evm::Result<U256> where T: Tracer, V: VMTracer {
+	) -> evm::Result<(U256, ReturnData)> where T: Tracer, V: VMTracer {
 		// backup used in case of running out of gas
 		self.state.checkpoint();
 
@@ -329,7 +329,7 @@ impl<'a, B: 'a + StateBackend, E: Engine + ?Sized> Executive<'a, B, E> {
 						);
 					}
 
-					Ok(params.gas - cost)
+					Ok((params.gas - cost, ReturnData::empty()))
 				}
 			} else {
 				// just drain the whole gas
@@ -376,13 +376,13 @@ impl<'a, B: 'a + StateBackend, E: Engine + ?Sized> Executive<'a, B, E> {
 
 				self.enact_result(&res, substate, unconfirmed_substate);
 				trace!(target: "executive", "enacted: substate={:?}\n", substate);
-				res.map(|r| r.gas_left)
+				res.map(|r| (r.gas_left, r.return_data))
 			} else {
 				// otherwise it's just a basic transaction, only do tracing, if necessary.
 				self.state.discard_checkpoint();
 
 				tracer.trace_call(trace_info, U256::zero(), trace_output, vec![]);
-				Ok(params.gas)
+				Ok((params.gas, ReturnData::empty()))
 			}
 		}
 	}
@@ -396,7 +396,7 @@ impl<'a, B: 'a + StateBackend, E: Engine + ?Sized> Executive<'a, B, E> {
 		substate: &mut Substate,
 		tracer: &mut T,
 		vm_tracer: &mut V,
-	) -> evm::Result<U256> where T: Tracer, V: VMTracer {
+	) -> evm::Result<(U256, ReturnData)> where T: Tracer, V: VMTracer {
 
 		let scheme = self.engine.create_address_scheme(self.info.number);
 		if scheme != CreateContractAddress::FromSenderAndNonce && self.state.exists_and_has_code(&params.address)? {
@@ -446,7 +446,7 @@ impl<'a, B: 'a + StateBackend, E: Engine + ?Sized> Executive<'a, B, E> {
 		};
 
 		self.enact_result(&res, substate, unconfirmed_substate);
-		res.map(|r| r.gas_left)
+		res.map(|r| (r.gas_left, r.return_data))
 	}
 
 	/// Finalizes the transaction (does refunds and suicides).
@@ -454,7 +454,7 @@ impl<'a, B: 'a + StateBackend, E: Engine + ?Sized> Executive<'a, B, E> {
 		&mut self,
 		t: &SignedTransaction,
 		mut substate: Substate,
-		result: evm::Result<U256>,
+		result: evm::Result<(U256, ReturnData)>,
 		output: Bytes,
 		trace: Vec<FlatTrace>,
 		vm_trace: Option<VMTrace>
@@ -468,7 +468,7 @@ impl<'a, B: 'a + StateBackend, E: Engine + ?Sized> Executive<'a, B, E> {
 		let refunds_bound = sstore_refunds + suicide_refunds;
 
 		// real ammount to refund
-		let gas_left_prerefund = match result { Ok(x) => x, _ => 0.into() };
+		let gas_left_prerefund = match result { Ok((x, _)) => x, _ => 0.into() };
 		let refunded = cmp::min(refunds_bound, (t.gas - gas_left_prerefund) >> 1);
 		let gas_left = gas_left_prerefund + refunded;
 
@@ -597,7 +597,7 @@ mod tests {
 		let engine = TestEngine::new(0);
 		let mut substate = Substate::new();
 
-		let gas_left = {
+		let (gas_left, _) = {
 			let mut ex = Executive::new(&mut state, &info, &engine);
 			ex.create(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer).unwrap()
 		};
@@ -655,7 +655,7 @@ mod tests {
 		let engine = TestEngine::new(0);
 		let mut substate = Substate::new();
 
-		let gas_left = {
+		let (gas_left, _) = {
 			let mut ex = Executive::new(&mut state, &info, &engine);
 			ex.create(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer).unwrap()
 		};
@@ -713,7 +713,7 @@ mod tests {
 		let mut tracer = ExecutiveTracer::default();
 		let mut vm_tracer = ExecutiveVMTracer::toplevel();
 
-		let gas_left = {
+		let (gas_left, _) = {
 			let mut ex = Executive::new(&mut state, &info, &engine);
 			let output = BytesRef::Fixed(&mut[0u8;0]);
 			ex.call(params, &mut substate, output, &mut tracer, &mut vm_tracer).unwrap()
@@ -822,7 +822,7 @@ mod tests {
 		let mut tracer = ExecutiveTracer::default();
 		let mut vm_tracer = ExecutiveVMTracer::toplevel();
 
-		let gas_left = {
+		let (gas_left, _) = {
 			let mut ex = Executive::new(&mut state, &info, &engine);
 			ex.create(params.clone(), &mut substate, &mut tracer, &mut vm_tracer).unwrap()
 		};
@@ -907,7 +907,7 @@ mod tests {
 		let engine = TestEngine::new(0);
 		let mut substate = Substate::new();
 
-		let gas_left = {
+		let (gas_left, _) = {
 			let mut ex = Executive::new(&mut state, &info, &engine);
 			ex.create(params, &mut substate, &mut NoopTracer, &mut NoopVMTracer).unwrap()
 		};
@@ -1018,7 +1018,7 @@ mod tests {
 		let engine = TestEngine::new(0);
 		let mut substate = Substate::new();
 
-		let gas_left = {
+		let (gas_left, _) = {
 			let mut ex = Executive::new(&mut state, &info, &engine);
 			ex.call(params, &mut substate, BytesRef::Fixed(&mut []), &mut NoopTracer, &mut NoopVMTracer).unwrap()
 		};
@@ -1062,7 +1062,7 @@ mod tests {
 		let engine = TestEngine::new(0);
 		let mut substate = Substate::new();
 
-		let gas_left = {
+		let (gas_left, _) = {
 			let mut ex = Executive::new(&mut state, &info, &engine);
 			ex.call(params, &mut substate, BytesRef::Fixed(&mut []), &mut NoopTracer, &mut NoopVMTracer).unwrap()
 		};
@@ -1267,7 +1267,7 @@ mod tests {
 		let mut substate = Substate::new();
 
 		let mut output = [0u8; 14];
-		let result = {
+		let (result, _) = {
 			let mut ex = Executive::new(&mut state, &info, &engine);
 			ex.call(params, &mut substate, BytesRef::Fixed(&mut output), &mut NoopTracer, &mut NoopVMTracer).unwrap()
 		};
diff --git a/ethcore/src/externalities.rs b/ethcore/src/externalities.rs
index 25ed0d042..22a80a3ba 100644
--- a/ethcore/src/externalities.rs
+++ b/ethcore/src/externalities.rs
@@ -21,7 +21,7 @@ use state::{Backend as StateBackend, State, Substate};
 use engines::Engine;
 use env_info::EnvInfo;
 use executive::*;
-use evm::{self, Schedule, Ext, ContractCreateResult, MessageCallResult, CreateContractAddress};
+use evm::{self, Schedule, Ext, ContractCreateResult, MessageCallResult, CreateContractAddress, ReturnData};
 use types::executed::CallType;
 use types::transaction::UNSIGNED_SENDER;
 use trace::{Tracer, VMTracer};
@@ -212,7 +212,7 @@ impl<'a, T: 'a, V: 'a, B: 'a, E: 'a> Ext for Externalities<'a, T, V, B, E>
 
 		// TODO: handle internal error separately
 		match ex.create(params, self.substate, self.tracer, self.vm_tracer) {
-			Ok(gas_left) => {
+			Ok((gas_left, _)) => {
 				self.substate.contracts_created.push(address.clone());
 				ContractCreateResult::Created(address, gas_left)
 			},
@@ -261,7 +261,7 @@ impl<'a, T: 'a, V: 'a, B: 'a, E: 'a> Ext for Externalities<'a, T, V, B, E>
 		let mut ex = Executive::from_parent(self.state, self.env_info, self.engine, self.depth);
 
 		match ex.call(params, self.substate, BytesRef::Fixed(output), self.tracer, self.vm_tracer) {
-			Ok(gas_left) => MessageCallResult::Success(gas_left),
+			Ok((gas_left, return_data)) => MessageCallResult::Success(gas_left, return_data),
 			_ => MessageCallResult::Failed
 		}
 	}
@@ -275,10 +275,10 @@ impl<'a, T: 'a, V: 'a, B: 'a, E: 'a> Ext for Externalities<'a, T, V, B, E>
 	}
 
 	#[cfg_attr(feature="dev", allow(match_ref_pats))]
-	fn ret(mut self, gas: &U256, data: &[u8]) -> evm::Result<U256>
+	fn ret(mut self, gas: &U256, data: &ReturnData) -> evm::Result<U256>
 		where Self: Sized {
 		let handle_copy = |to: &mut Option<&mut Bytes>| {
-			to.as_mut().map(|b| **b = data.to_owned());
+			to.as_mut().map(|b| **b = data.to_vec());
 		};
 		match self.output {
 			OutputPolicy::Return(BytesRef::Fixed(ref mut slice), ref mut copy) => {
@@ -292,7 +292,7 @@ impl<'a, T: 'a, V: 'a, B: 'a, E: 'a> Ext for Externalities<'a, T, V, B, E>
 				handle_copy(copy);
 
 				vec.clear();
-				vec.extend_from_slice(data);
+				vec.extend_from_slice(&*data);
 				Ok(*gas)
 			},
 			OutputPolicy::InitContract(ref mut copy) => {
diff --git a/ethcore/src/json_tests/executive.rs b/ethcore/src/json_tests/executive.rs
index 86442179b..b21259090 100644
--- a/ethcore/src/json_tests/executive.rs
+++ b/ethcore/src/json_tests/executive.rs
@@ -21,7 +21,7 @@ use executive::*;
 use engines::Engine;
 use env_info::EnvInfo;
 use evm;
-use evm::{Schedule, Ext, Finalize, VMType, ContractCreateResult, MessageCallResult, CreateContractAddress};
+use evm::{Schedule, Ext, Finalize, VMType, ContractCreateResult, MessageCallResult, CreateContractAddress, ReturnData};
 use externalities::*;
 use types::executed::CallType;
 use tests::helpers::*;
@@ -142,7 +142,7 @@ impl<'a, T: 'a, V: 'a, B: 'a, E: 'a> Ext for TestExt<'a, T, V, B, E>
 			gas_limit: *gas,
 			value: value.unwrap()
 		});
-		MessageCallResult::Success(*gas)
+		MessageCallResult::Success(*gas, ReturnData::empty())
 	}
 
 	fn extcode(&self, address: &Address) -> trie::Result<Arc<Bytes>>  {
@@ -157,7 +157,7 @@ impl<'a, T: 'a, V: 'a, B: 'a, E: 'a> Ext for TestExt<'a, T, V, B, E>
 		self.ext.log(topics, data)
 	}
 
-	fn ret(self, gas: &U256, data: &[u8]) -> Result<U256, evm::Error> {
+	fn ret(self, gas: &U256, data: &ReturnData) -> Result<U256, evm::Error> {
 		self.ext.ret(gas, data)
 	}
 
diff --git a/ethcore/src/spec/spec.rs b/ethcore/src/spec/spec.rs
index 915ff91b0..819964aef 100644
--- a/ethcore/src/spec/spec.rs
+++ b/ethcore/src/spec/spec.rs
@@ -72,6 +72,8 @@ pub struct CommonParams {
 	pub eip210_contract_code: Bytes,
 	/// Gas allocated for EIP-210 blockhash update.
 	pub eip210_contract_gas: U256,
+	/// Number of first block where EIP-211 (Metropolis: RETURNDATASIZE/RETURNDATACOPY) rules begin.
+	pub eip211_transition: BlockNumber,
 }
 
 impl From<ethjson::spec::Params> for CommonParams {
@@ -94,6 +96,7 @@ impl From<ethjson::spec::Params> for CommonParams {
 				|| DEFAULT_BLOCKHASH_CONTRACT.from_hex().expect("Default BLOCKHASH contract is valid"),
 				Into::into),
 			eip210_contract_gas: p.eip210_contract_gas.map_or(1000000.into(), Into::into),
+			eip211_transition: p.eip211_transition.map_or(BlockNumber::max_value(), Into::into),
 		}
 	}
 }
diff --git a/json/src/spec/params.rs b/json/src/spec/params.rs
index e5029f4f2..fc69435c9 100644
--- a/json/src/spec/params.rs
+++ b/json/src/spec/params.rs
@@ -75,6 +75,9 @@ pub struct Params {
 	/// See `CommonParams` docs.
 	#[serde(rename="eip210ContractGas")]
 	pub eip210_contract_gas: Option<Uint>,
+	/// See `CommonParams` docs.
+	#[serde(rename="eip211Transition")]
+	pub eip211_transition: Option<Uint>,
 }
 
 #[cfg(test)]