With 1.34, I was using the pattern described by Robert (http://lists.boost.org/boost-users/2006/01/16293.php) with non-intrusive serialization. In short, the serialization functions are merely declared in the header files. They are implemented in the .cpp file, and then explicitly instantiated for each archive type I'm using. However, with 1.35, this no longer works. The export macros create an instance of the guid initializer as follows: export.hpp:150 BOOST_PP_CAT(boost_serialization_guid_initializer_, __LINE__) However, this gives me redefinition errors in the following situaion: ClassA.h -------- (line 1:) BOOST_CLASS_EXPORT(ClassA); ClassB.h -------- (line 1: )BOOST_CLASS_EXPORT(ClassB); main.cpp #include <ClassA.h> #include <ClassB.h> (create an archive instance and attempt to serialize) ------------------------------- As you can see, two objects, both named boost_serialization_guid_initializer_1, will be created, and the compiler (MSVC80) will give me a redefinition error. I honestly have no idea what's going on. This is so obvious, it has to mean that I'm organizing my code in some weird fashion. Thanks! Dan