diff --git a/Cargo.lock b/Cargo.lock
index 4dee89f7..f2fa8ec6 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -530,6 +530,7 @@ dependencies = [
  "parking_lot 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "primitives 0.1.0",
  "serialization 0.1.0",
+ "test-data 0.1.0",
 ]
 
 [[package]]
diff --git a/test-data/src/lib.rs b/test-data/src/lib.rs
index 4654f936..9499ca0e 100644
--- a/test-data/src/lib.rs
+++ b/test-data/src/lib.rs
@@ -8,3 +8,17 @@ pub fn block1() -> Block {
 	let block: Block = "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".into();
 	block
 }
+
+// https://webbtc.com/block/00000000839a8e6886ab5951d76f411475428afc90947ee320161bbf18eb6048
+// height 1
+pub fn block_h1() -> Block {
+	let block: Block = "010000006fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000982051fd1e4ba744bbbe680e1fee14677ba1a3c3540bf7b1cdb606e857233e0e61bc6649ffff001d01e362990101000000010000000000000000000000000000000000000000000000000000000000000000ffffffff0704ffff001d0104ffffffff0100f2052a0100000043410496b538e853519c726a2c91e61ec11600ae1390813a627c66fb8be7947be63c52da7589379515d4e0a604f8141781e62294721166bf621e73a82cbf2342c858eeac00000000".into();
+	block
+}
+
+// https://webbtc.com/block/000000006a625f06636b8bb6ac7b960a8d03705d1ace08b1a19da3fdcc99ddbd.hex
+// height 2
+pub fn block_h2() -> Block {
+	let block: Block = "010000004860eb18bf1b1620e37e9490fc8a427514416fd75159ab86688e9a8300000000d5fdcc541e25de1c7a5addedf24858b8bb665c9f36ef744ee42c316022c90f9bb0bc6649ffff001d08d2bd610101000000010000000000000000000000000000000000000000000000000000000000000000ffffffff0704ffff001d010bffffffff0100f2052a010000004341047211a824f55b505228e4c3d5194c1fcfaa15a456abdf37f9b9d97a4040afc073dee6c89064984f03385237d92167c13e236446b417ab79a0fcae412ae3316b77ac00000000".into();
+	block
+}
diff --git a/verification/Cargo.toml b/verification/Cargo.toml
index cbc2b687..1bf4b4b1 100644
--- a/verification/Cargo.toml
+++ b/verification/Cargo.toml
@@ -11,3 +11,4 @@ chain = { path = "../chain"  }
 serialization = { path = "../serialization" }
 parking_lot = "0.3"
 linked-hash-map = "0.3"
+test-data = { path = "../test-data" }
diff --git a/verification/src/lib.rs b/verification/src/lib.rs
index e0fdbcfa..89478523 100644
--- a/verification/src/lib.rs
+++ b/verification/src/lib.rs
@@ -9,6 +9,8 @@ extern crate linked_hash_map;
 
 #[cfg(test)]
 extern crate ethcore_devtools as devtools;
+#[cfg(test)]
+extern crate test_data;
 
 mod queue;
 
@@ -67,6 +69,6 @@ pub enum BlockStatus {
 pub type VerificationResult = Result<Chain, Error>;
 
 /// Interface for block verification
-pub trait Verify {
+pub trait Verify : Send + Sync {
 	fn verify(&self, block: &chain::Block) -> VerificationResult;
 }
diff --git a/verification/src/queue.rs b/verification/src/queue.rs
index 02deef5d..674554dc 100644
--- a/verification/src/queue.rs
+++ b/verification/src/queue.rs
@@ -7,6 +7,8 @@ use linked_hash_map::LinkedHashMap;
 use parking_lot::RwLock;
 use std::collections::HashSet;
 
+const MAX_PENDING_PRESET: usize = 128;
+
 pub struct VerifiedBlock {
 	pub chain: Chain,
 	pub block: Block,
@@ -18,6 +20,15 @@ impl VerifiedBlock {
 	}
 }
 
+#[derive(Debug)]
+/// Queue errors
+pub enum Error {
+	/// Queue is currently full
+	Full,
+	/// There is already block in the queue
+	Duplicate,
+}
+
 /// Verification queue
 pub struct Queue {
 	verifier: Box<Verify>,
@@ -69,24 +80,121 @@ impl Queue {
 		else if self.items.read().contains_key(hash) { BlockStatus::Pending }
 		else { BlockStatus::Absent }
 	}
+
+	pub fn max_pending(&self) -> usize {
+		// todo: later might be calculated with lazy-static here based on memory usage
+		MAX_PENDING_PRESET
+	}
+
+	pub fn push(&self, block: Block) -> Result<(), Error> {
+		let hash = block.hash();
+
+		if self.block_status(&hash) != BlockStatus::Absent { return Err(Error::Duplicate) }
+
+		let mut items = self.items.write();
+		if items.len() > self.max_pending() { return Err(Error::Full) }
+		items.insert(hash, block);
+
+		Ok(())
+	}
 }
 
 #[cfg(test)]
 mod tests {
 	use super::Queue;
-	use super::super::{BlockStatus, VerificationResult, Verify, Chain};
+	use super::super::{BlockStatus, VerificationResult, Verify, Chain, Error as VerificationError};
 	use chain::Block;
 	use primitives::hash::H256;
+	use test_data;
 
 	struct FacileVerifier;
 	impl Verify for FacileVerifier {
 		fn verify(&self, _block: &Block) -> VerificationResult { Ok(Chain::Main) }
 	}
 
+	struct EvilVerifier;
+	impl Verify for EvilVerifier {
+		fn verify(&self, _block: &Block) -> VerificationResult { Err(VerificationError::Empty) }
+	}
+
 	#[test]
 	fn new() {
 		let queue = Queue::new(Box::new(FacileVerifier));
 		assert_eq!(queue.block_status(&H256::from(0u8)), BlockStatus::Absent);
 	}
 
+	#[test]
+	fn push() {
+		let queue = Queue::new(Box::new(FacileVerifier));
+		let block = test_data::block1();
+		let hash = block.hash();
+
+		queue.push(block).unwrap();
+
+		assert_eq!(queue.block_status(&hash), BlockStatus::Pending);
+	}
+
+	#[test]
+	fn push_duplicate() {
+		let queue = Queue::new(Box::new(FacileVerifier));
+		let block = test_data::block1();
+		let dup_block = test_data::block1();
+
+		queue.push(block).unwrap();
+		let second_push = queue.push(dup_block);
+
+		assert!(second_push.is_err());
+	}
+
+	#[test]
+	fn process_happy() {
+		let queue = Queue::new(Box::new(FacileVerifier));
+		let block = test_data::block1();
+		let hash = block.hash();
+
+		queue.push(block).unwrap();
+		queue.process();
+
+		assert_eq!(queue.block_status(&hash), BlockStatus::Valid);
+	}
+
+	#[test]
+	fn process_unhappy() {
+		let queue = Queue::new(Box::new(EvilVerifier));
+		let block = test_data::block1();
+		let hash = block.hash();
+
+		queue.push(block).unwrap();
+		queue.process();
+
+		assert_eq!(queue.block_status(&hash), BlockStatus::Invalid);
+	}
+
+	#[test]
+	fn process_async() {
+		use std::thread;
+		use std::sync::Arc;
+
+		let queue = Arc::new(Queue::new(Box::new(FacileVerifier)));
+
+		let t1_queue = queue.clone();
+		let t1_handle = thread::spawn(move || {
+			let block_h1 = test_data::block_h1();
+			t1_queue.push(block_h1).unwrap();
+			t1_queue.process();
+		});
+
+		let t2_queue = queue.clone();
+		let t2_handle = thread::spawn(move || {
+			let block_h2 = test_data::block_h2();
+			t2_queue.push(block_h2).unwrap();
+			t2_queue.process();
+		});
+
+		t1_handle.join().unwrap();
+		t2_handle.join().unwrap();
+
+		assert_eq!(queue.block_status(&test_data::block_h1().hash()), BlockStatus::Valid);
+		assert_eq!(queue.block_status(&test_data::block_h2().hash()), BlockStatus::Valid);
+	}
 }