Hello, I have moved all serialization code in a separate static library that I called serialization. This, in my case, depends on mpi. The headers in this static library: 1. include <boost/serialization/export.hpp> 2. include the definition of the derived class being serialized 3. declare a template function serialize() that takes a reference to the derived class being serialized in the boost::serialization namespace 4. invoke the BOOST_CLASS_EXPORT_KEY(<derivedclass>) macro at the global namespace scope The corresponding source files in this static library: 1. include the header 2. define the function template serialize() 3. explicitly instantiate the serialize() function with all the archives used: mpi::packed_iarchive and mpi::packed_oarchive in the boost::serialization namespace 4. invoke the BOOST_CLASS_EXPORT_IMPLEMENT(<derivedclass>) macro at the global namespace scope The main program links against this static library, and invokes a mpi function (broadcast) that serializes by the base pointer. The base class is polymorphic. All class derivations are public. Debugging, the code reaches : archive/detail/oserializer.hpp boost::archive::detail::save_pointer_type<boost::mpi::packed_oarchive>::poly morphic::save<baseclass>(boost::mpi::packed_oarchive & ar={...}, baseclass& t={...}) Line 400 + 0x38 bytes where NULL==true_type However, looking at the t argument of save(), it shows that is the correct derived object. But the type T is the base class. What am I missing? regards,