I running into an issue where an irecv followed by a send results in deadlock. A simple test case, class Item { private: friend class boost::serialization::access; template<class Archive> void serialize(Archive& ar, const unsigned int version) { ar & val; } public: int val; Item() : val(1) { } }; struct Receipt { boost::mpi::request request; std::vector<Item> items; }; int main(int argc, char **argv) { mpi::environment env(argc, argv); mpi::communicator world; Receipt receipt; vector<Item> msg(100000); int other = world.rank() == 0 ? 1 : 0; cout << world.rank() << " irecv from " << other << endl; receipt.request = world.irecv(other, 0, receipt.items); cout << world.rank() << " sending to " << other << endl; world.send(other, 0, msg); receipt.request.wait(); cout << "Done" << endl; } Run with mpirun -np 2, this never completes. It does complete with vector<Item> msg(10) however. Nick