diff --git a/alethzero/MainWin.cpp b/alethzero/MainWin.cpp
index 5a47d991a..c85685d92 100644
--- a/alethzero/MainWin.cpp
+++ b/alethzero/MainWin.cpp
@@ -1355,7 +1355,7 @@ void Main::on_blocks_currentItemChanged()
 			s << "&nbsp;&emsp;&nbsp;Children: <b>" << details.children.size() << "</b></h5>";
 			s << "<br/>Gas used/limit: <b>" << info.gasUsed << "</b>/<b>" << info.gasLimit << "</b>";
 			s << "<br/>Coinbase: <b>" << pretty(info.coinbaseAddress).toHtmlEscaped().toStdString() << "</b> " << info.coinbaseAddress;
-			s << "<br/>Seed hash: <b>" << info.seedHash << "</b>";
+			s << "<br/>Seed hash: <b>" << info.seedHash() << "</b>";
 			s << "<br/>Mix hash: <b>" << info.mixHash << "</b>";
 			s << "<br/>Nonce: <b>" << info.nonce << "</b>";
 			s << "<br/>Hash w/o nonce: <b>" << info.headerHash(WithoutNonce) << "</b>";
@@ -1381,7 +1381,7 @@ void Main::on_blocks_currentItemChanged()
 				s << line << "Parent: <b>" << uncle.parentHash << "</b>";
 				s << line << "Number: <b>" << uncle.number << "</b>";
 				s << line << "Coinbase: <b>" << pretty(uncle.coinbaseAddress).toHtmlEscaped().toStdString() << "</b> " << uncle.coinbaseAddress;
-				s << line << "Seed hash: <b>" << uncle.seedHash << "</b>";
+				s << line << "Seed hash: <b>" << uncle.seedHash() << "</b>";
 				s << line << "Mix hash: <b>" << uncle.mixHash << "</b>";
 				s << line << "Nonce: <b>" << uncle.nonce << "</b>";
 				s << line << "Hash w/o nonce: <b>" << uncle.headerHash(WithoutNonce) << "</b>";
diff --git a/libethcore/BlockInfo.cpp b/libethcore/BlockInfo.cpp
index 0f37294c2..654dd9e1a 100644
--- a/libethcore/BlockInfo.cpp
+++ b/libethcore/BlockInfo.cpp
@@ -55,12 +55,20 @@ void BlockInfo::setEmpty()
 	gasUsed = 0;
 	timestamp = 0;
 	extraData.clear();
-	seedHash = h256();
 	mixHash = h256();
 	nonce = Nonce();
+	m_seedHash = h256();
 	hash = headerHash(WithNonce);
 }
 
+h256 BlockInfo::seedHash() const
+{
+	if (!m_seedHash)
+		for (u256 n = number; n >= c_epochDuration; n -= c_epochDuration)
+			m_seedHash = sha3(m_seedHash);
+	return m_seedHash;
+}
+
 BlockInfo BlockInfo::fromHeader(bytesConstRef _block, Strictness _s)
 {
 	BlockInfo ret;
@@ -77,9 +85,9 @@ h256 BlockInfo::headerHash(IncludeNonce _n) const
 
 void BlockInfo::streamRLP(RLPStream& _s, IncludeNonce _n) const
 {
-	_s.appendList(_n == WithNonce ? 16 : 14)
+	_s.appendList(_n == WithNonce ? 15 : 13)
 		<< parentHash << sha3Uncles << coinbaseAddress << stateRoot << transactionsRoot << receiptsRoot << logBloom
-		<< difficulty << number << gasLimit << gasUsed << timestamp << extraData << seedHash;
+		<< difficulty << number << gasLimit << gasUsed << timestamp << extraData;
 	if (_n == WithNonce)
 		_s << mixHash << nonce;
 }
@@ -109,9 +117,8 @@ void BlockInfo::populateFromHeader(RLP const& _header, Strictness _s)
 		gasUsed = _header[field = 10].toInt<u256>();
 		timestamp = _header[field = 11].toInt<u256>();
 		extraData = _header[field = 12].toBytes();
-		seedHash = _header[field = 13].toHash<h256>(RLP::VeryStrict);
-		mixHash = _header[field = 14].toHash<h256>(RLP::VeryStrict);
-		nonce = _header[field = 15].toHash<Nonce>(RLP::VeryStrict);
+		mixHash = _header[field = 13].toHash<h256>(RLP::VeryStrict);
+		nonce = _header[field = 14].toHash<Nonce>(RLP::VeryStrict);
 	}
 
 	catch (Exception const& _e)
@@ -188,12 +195,6 @@ void BlockInfo::populateFromParent(BlockInfo const& _parent)
 	gasLimit = calculateGasLimit(_parent);
 	gasUsed = 0;
 	difficulty = calculateDifficulty(_parent);
-	seedHash = calculateSeedHash(_parent);
-}
-
-h256 BlockInfo::calculateSeedHash(BlockInfo const& _parent) const
-{
-	return number % c_epochDuration == 0 ? sha3(_parent.seedHash.asBytes()) : _parent.seedHash;
 }
 
 u256 BlockInfo::calculateGasLimit(BlockInfo const& _parent) const
@@ -222,9 +223,6 @@ void BlockInfo::verifyParent(BlockInfo const& _parent) const
 		gasLimit > _parent.gasLimit * (c_gasLimitBoundDivisor + 1) / c_gasLimitBoundDivisor)
 		BOOST_THROW_EXCEPTION(InvalidGasLimit() << errinfo_min((bigint)_parent.gasLimit * (c_gasLimitBoundDivisor - 1) / c_gasLimitBoundDivisor) << errinfo_got((bigint)gasLimit) << errinfo_max((bigint)_parent.gasLimit * (c_gasLimitBoundDivisor + 1) / c_gasLimitBoundDivisor));
 
-	if (seedHash != calculateSeedHash(_parent))
-		BOOST_THROW_EXCEPTION(InvalidSeedHash());
-
 	// Check timestamp is after previous timestamp.
 	if (parentHash)
 	{
diff --git a/libethcore/BlockInfo.h b/libethcore/BlockInfo.h
index 20134f059..714adb375 100644
--- a/libethcore/BlockInfo.h
+++ b/libethcore/BlockInfo.h
@@ -67,6 +67,7 @@ enum Strictness
 struct BlockInfo
 {
 public:
+	// TODO: make them all private!
 	h256 hash;						///< SHA3 hash of the block header! Not serialised (the only member not contained in a block header).
 	h256 parentHash;
 	h256 sha3Uncles;
@@ -82,7 +83,6 @@ public:
 	u256 timestamp;
 	bytes extraData;
 	h256 mixHash;
-	h256 seedHash;
 	Nonce nonce;
 
 	BlockInfo();
@@ -113,7 +113,6 @@ public:
 				timestamp == _cmp.timestamp &&
 				extraData == _cmp.extraData &&
 				mixHash == _cmp.mixHash &&
-				seedHash == _cmp.seedHash &&
 				nonce == _cmp.nonce;
 	}
 	bool operator!=(BlockInfo const& _cmp) const { return !operator==(_cmp); }
@@ -129,18 +128,21 @@ public:
 
 	u256 calculateDifficulty(BlockInfo const& _parent) const;
 	u256 calculateGasLimit(BlockInfo const& _parent) const;
-	h256 calculateSeedHash(BlockInfo const& _parent) const;
+	h256 seedHash() const;
 
 	/// sha3 of the header only.
 	h256 headerHash(IncludeNonce _n) const;
 	void streamRLP(RLPStream& _s, IncludeNonce _n) const;
+
+private:
+	mutable h256 m_seedHash;
 };
 
 inline std::ostream& operator<<(std::ostream& _out, BlockInfo const& _bi)
 {
 	_out << _bi.hash << " " << _bi.parentHash << " " << _bi.sha3Uncles << " " << _bi.coinbaseAddress << " " << _bi.stateRoot << " " << _bi.transactionsRoot << " " <<
 			_bi.receiptsRoot << " " << _bi.logBloom << " " << _bi.difficulty << " " << _bi.number << " " << _bi.gasLimit << " " <<
-			_bi.gasUsed << " " << _bi.timestamp << " " << _bi.mixHash << " " << _bi.seedHash << " " << _bi.nonce;
+			_bi.gasUsed << " " << _bi.timestamp << " " << _bi.mixHash << " " << _bi.nonce << " (" << _bi.seedHash() << ")";
 	return _out;
 }
 
diff --git a/libethcore/Common.cpp b/libethcore/Common.cpp
index 8bd4ef143..c821bf057 100644
--- a/libethcore/Common.cpp
+++ b/libethcore/Common.cpp
@@ -32,7 +32,7 @@ namespace dev
 namespace eth
 {
 
-const unsigned c_protocolVersion = 56;
+const unsigned c_protocolVersion = 57;
 const unsigned c_databaseBaseVersion = 8;
 #if ETH_FATDB
 const unsigned c_databaseVersionModifier = 1000;
diff --git a/libethcore/Ethasher.cpp b/libethcore/Ethasher.cpp
index 52a1d17d7..f80277cb2 100644
--- a/libethcore/Ethasher.cpp
+++ b/libethcore/Ethasher.cpp
@@ -25,11 +25,12 @@
 #include <array>
 #include <random>
 #include <thread>
+#include <libdevcore/Common.h>
 #include <libdevcore/Guards.h>
 #include <libdevcore/Log.h>
 #include <libdevcrypto/CryptoPP.h>
 #include <libdevcrypto/FileSystem.h>
-#include <libdevcore/Common.h>
+#include <libethcore/Params.h>
 #include <libethash/ethash.h>
 #include "BlockInfo.h"
 #include "Ethasher.h"
@@ -49,19 +50,19 @@ bytes const& Ethasher::cache(BlockInfo const& _header)
 		throw std::invalid_argument( error.str() );
  	}
 
-	if (!m_caches.count(_header.seedHash))
+	if (!m_caches.count(_header.seedHash()))
 	{
 		ethash_params p = params((unsigned)_header.number);
-		m_caches[_header.seedHash].resize(p.cache_size);
-		ethash_prep_light(m_caches[_header.seedHash].data(), &p, _header.seedHash.data());
+		m_caches[_header.seedHash()].resize(p.cache_size);
+		ethash_prep_light(m_caches[_header.seedHash()].data(), &p, _header.seedHash().data());
 	}
-	return m_caches[_header.seedHash];
+	return m_caches[_header.seedHash()];
 }
 
 bytesConstRef Ethasher::full(BlockInfo const& _header)
 {
 	RecursiveGuard l(x_this);
-	if (!m_fulls.count(_header.seedHash))
+	if (!m_fulls.count(_header.seedHash()))
 	{
 		if (!m_fulls.empty())
 		{
@@ -71,18 +72,18 @@ bytesConstRef Ethasher::full(BlockInfo const& _header)
 		try {
 			boost::filesystem::create_directories(getDataDir() + "/ethashcache");
 		} catch (...) {}
-		std::string memoFile = getDataDir() + "/ethashcache/" + toHex(_header.seedHash.ref().cropped(0, 4)) + ".full";
-		m_fulls[_header.seedHash] = contentsNew(memoFile);
-		if (!m_fulls[_header.seedHash])
+		std::string memoFile = getDataDir() + "/ethashcache/" + toHex(_header.seedHash().ref().cropped(0, 4)) + ".full";
+		m_fulls[_header.seedHash()] = contentsNew(memoFile);
+		if (!m_fulls[_header.seedHash()])
 		{
 			ethash_params p = params((unsigned)_header.number);
-			m_fulls[_header.seedHash] = bytesRef(new byte[p.full_size], p.full_size);
+			m_fulls[_header.seedHash()] = bytesRef(new byte[p.full_size], p.full_size);
 			auto c = cache(_header);
-			ethash_prep_full(m_fulls[_header.seedHash].data(), &p, c.data());
-			writeFile(memoFile, m_fulls[_header.seedHash]);
+			ethash_prep_full(m_fulls[_header.seedHash()].data(), &p, c.data());
+			writeFile(memoFile, m_fulls[_header.seedHash()]);
 		}
 	}
-	return m_fulls[_header.seedHash];
+	return m_fulls[_header.seedHash()];
 }
 
 ethash_params Ethasher::params(BlockInfo const& _header)
diff --git a/test/blockchain.cpp b/test/blockchain.cpp
index eca08d09e..045f2de5b 100644
--- a/test/blockchain.cpp
+++ b/test/blockchain.cpp
@@ -313,7 +313,6 @@ void doBlockchainTests(json_spirit::mValue& _v, bool _fillin)
 				BOOST_CHECK_MESSAGE(blockHeaderFromFields.timestamp == blockFromRlp.timestamp, "timestamp in given RLP not matching the block timestamp!");
 				BOOST_CHECK_MESSAGE(blockHeaderFromFields.extraData == blockFromRlp.extraData, "extraData in given RLP not matching the block extraData!");
 				BOOST_CHECK_MESSAGE(blockHeaderFromFields.mixHash == blockFromRlp.mixHash, "mixHash in given RLP not matching the block mixHash!");
-				BOOST_CHECK_MESSAGE(blockHeaderFromFields.seedHash == blockFromRlp.seedHash, "transactionsRoot in given RLP not matching the block transactionsRoot!");
 				BOOST_CHECK_MESSAGE(blockHeaderFromFields.nonce == blockFromRlp.nonce, "nonce in given RLP not matching the block nonce!");
 
 				BOOST_CHECK_MESSAGE(blockHeaderFromFields == blockFromRlp, "However, blockHeaderFromFields != blockFromRlp!");
@@ -466,9 +465,6 @@ bytes createBlockRLPFromFields(mObject& _tObj)
 	if (_tObj.count("extraData"))
 		rlpStream << fromHex(_tObj["extraData"].get_str());
 
-	if (_tObj.count("seedHash"))
-		rlpStream << importByteArray(_tObj["seedHash"].get_str());
-
 	if (_tObj.count("mixHash"))
 		rlpStream << importByteArray(_tObj["mixHash"].get_str());
 
@@ -527,9 +523,6 @@ void overwriteBlockHeader(BlockInfo& _current_BlockHeader, mObject& _blObj)
 		if (_blObj["blockHeader"].get_obj().count("mixHash"))
 			tmp.mixHash = h256(_blObj["blockHeader"].get_obj()["mixHash"].get_str());
 
-		if (_blObj["blockHeader"].get_obj().count("seedHash"))
-			tmp.seedHash = h256(_blObj["blockHeader"].get_obj()["seedHash"].get_str());
-
 		// find new valid nonce
 
 		if (tmp != _current_BlockHeader)
@@ -609,7 +602,6 @@ void writeBlockHeaderToJson(mObject& _o, const BlockInfo& _bi)
 	_o["timestamp"] = toString(_bi.timestamp);
 	_o["extraData"] ="0x" + toHex(_bi.extraData);
 	_o["mixHash"] = toString(_bi.mixHash);
-	_o["seedHash"] = toString(_bi.seedHash);
 	_o["nonce"] = toString(_bi.nonce);
 	_o["hash"] = toString(_bi.hash);
 }