At least in the serialization library it can occur that the library calls back into the users code. Also there are lots of c style asserts. These can be helpful in debugging users code. Finally, the release libraries collapse inline code to the point its impossible to figure out how one got to where he did. Sometimes debug and release code is built with incompatible options. A users code built for debug might call a function that was inlined in the release version of the library and left out of line in the debug version of the library. If this happens, an application built for debug may fail to link with one built for release - even though they use the same headers. So there are case where the debug libraries are useful for things other than debugging the library itself. Robert Ramey