diff --git a/message-broker/src/lib.rs b/message-broker/src/lib.rs
index 47733e811a..31acd3c1ca 100644
--- a/message-broker/src/lib.rs
+++ b/message-broker/src/lib.rs
@@ -21,15 +21,19 @@
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
-use sp_std::prelude::*;
+use frame_support::{
+	decl_module, decl_storage, storage,
+	weights::{DispatchClass, Weight},
+	traits::Get,
+	StorageValue,
+};
 use frame_system::ensure_none;
-use frame_support::{decl_module, storage, weights::DispatchClass};
 use sp_inherents::{InherentData, InherentIdentifier, MakeFatalError, ProvideInherent};
+use sp_std::{prelude::*, cmp};
 
 use cumulus_primitives::{
 	inherents::{DownwardMessagesType, DOWNWARD_MESSAGES_IDENTIFIER},
-	well_known_keys,
-	DownwardMessageHandler, InboundDownwardMessage,
+	well_known_keys, DownwardMessageHandler, InboundDownwardMessage, UpwardMessage,
 };
 
 /// Configuration trait of the message broker pallet.
@@ -38,6 +42,12 @@ pub trait Trait: frame_system::Trait {
 	type DownwardMessageHandlers: DownwardMessageHandler;
 }
 
+decl_storage! {
+	trait Store for Module<T: Trait> as MessageBroker {
+		PendingUpwardMessages: Vec<UpwardMessage>;
+	}
+}
+
 decl_module! {
 	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
 		/// An entrypoint for an inherent to deposit downward messages into the runtime. It accepts
@@ -58,6 +68,40 @@ decl_module! {
 				&messages_len,
 			);
 		}
+
+		fn on_initialize() -> Weight {
+			// Reads and writes performed by `on_finalize`.
+			T::DbWeight::get().reads_writes(1, 2)
+		}
+
+		fn on_finalize() {
+			// TODO: this should be not a constant, but sourced from the relay-chain configuration.
+			const UMP_MSG_NUM_PER_CANDIDATE: usize = 5;
+
+			<Self as Store>::PendingUpwardMessages::mutate(|up| {
+				let num = cmp::min(UMP_MSG_NUM_PER_CANDIDATE, up.len());
+				storage::unhashed::put(
+					well_known_keys::UPWARD_MESSAGES,
+					&up[0..num],
+				);
+				*up = up.split_off(num);
+			});
+		}
+	}
+}
+
+/// An error that can be raised upon sending an upward message.
+pub enum SendUpErr {
+	/// The message sent is too big.
+	TooBig,
+}
+
+impl<T: Trait> Module<T> {
+	pub fn send_upward_message(message: UpwardMessage) -> Result<(), SendUpErr> {
+		// TODO: check the message against the limit. The limit should be sourced from the
+		// relay-chain configuration.
+		<Self as Store>::PendingUpwardMessages::append(message);
+		Ok(())
 	}
 }
 
diff --git a/primitives/src/lib.rs b/primitives/src/lib.rs
index e8f9d90b31..69480c79e4 100644
--- a/primitives/src/lib.rs
+++ b/primitives/src/lib.rs
@@ -20,11 +20,7 @@
 
 pub use polkadot_core_primitives as relay_chain;
 pub use polkadot_core_primitives::InboundDownwardMessage;
-/// A generic upward message from a Parachain to the Relay Chain.
-///
-/// It is "generic" in such a way, that the actual message is encoded in the `data` field.
-/// Besides the `data` it also holds the `origin` of the message.
-pub use polkadot_parachain::primitives::UpwardMessage as GenericUpwardMessage;
+pub use polkadot_parachain::primitives::UpwardMessage;
 pub use polkadot_parachain::primitives::{Id as ParaId, ValidationParams};
 pub use polkadot_primitives::v1::{
 	PersistedValidationData, TransientValidationData, ValidationData,
@@ -54,7 +50,7 @@ pub mod inherents {
 pub mod well_known_keys {
 	/// The storage key for the upward messages.
 	///
-	/// The upward messages are stored as SCALE encoded `Vec<GenericUpwardMessage>`.
+	/// The upward messages are stored as SCALE encoded `Vec<UpwardMessage>`.
 	pub const UPWARD_MESSAGES: &'static [u8] = b":cumulus_upward_messages:";
 
 	/// Current validation data.
diff --git a/rococo-parachains/runtime/src/lib.rs b/rococo-parachains/runtime/src/lib.rs
index b86db734e3..1d72f04890 100644
--- a/rococo-parachains/runtime/src/lib.rs
+++ b/rococo-parachains/runtime/src/lib.rs
@@ -218,7 +218,7 @@ construct_runtime! {
 		Sudo: pallet_sudo::{Module, Call, Storage, Config<T>, Event<T>},
 		RandomnessCollectiveFlip: pallet_randomness_collective_flip::{Module, Call, Storage},
 		ParachainUpgrade: cumulus_parachain_upgrade::{Module, Call, Storage, Inherent, Event},
-		MessageBroker: cumulus_message_broker::{Module, Call, Inherent},
+		MessageBroker: cumulus_message_broker::{Module, Storage, Call, Inherent},
 		TransactionPayment: pallet_transaction_payment::{Module, Storage},
 		ParachainInfo: parachain_info::{Module, Storage, Config},
 	}
diff --git a/runtime/src/validate_block/implementation.rs b/runtime/src/validate_block/implementation.rs
index 600fa0c066..e850dd2b42 100644
--- a/runtime/src/validate_block/implementation.rs
+++ b/runtime/src/validate_block/implementation.rs
@@ -31,7 +31,7 @@ use cumulus_primitives::{
 	well_known_keys::{
 		NEW_VALIDATION_CODE, PROCESSED_DOWNWARD_MESSAGES, UPWARD_MESSAGES, VALIDATION_DATA,
 	},
-	GenericUpwardMessage, ValidationData,
+	UpwardMessage, ValidationData,
 };
 use sp_externalities::{set_and_run_with_externalities};
 use sp_externalities::{Externalities, ExtensionStore, Error, Extension};
@@ -148,7 +148,7 @@ pub fn validate_block<B: BlockT, E: ExecuteBlock<B>>(params: ValidationParams) -
 
 	// Extract potential upward messages from the storage.
 	let upward_messages = match overlay.storage(UPWARD_MESSAGES).flatten() {
-		Some(encoded) => Vec::<GenericUpwardMessage>::decode(&mut &encoded[..])
+		Some(encoded) => Vec::<UpwardMessage>::decode(&mut &encoded[..])
 			.expect("Upward messages vec is not correctly encoded in the storage!"),
 		None => Vec::new(),
 	};