Hi! It seems to me, that the following string should be inserted to intrusive_ptr.hpp <string> #include </string> Following code can not be compiled without this string under MSVC6SP5(with STLPort) <code> # if defined(BOOST_MSVC) && BOOST_WORKAROUND(BOOST_MSVC, <= 1200 && __SGI_STL_PORT) // MSVC6 has problems finding std::basic_ostream through the using declaration in namespace _STL using std::basic_ostream; template basic_ostream & operator<< (basic_ostream & os, intrusive_ptr<Y> const & p) # else template std::basic_ostream & operator<< (std::basic_ostream & os, intrusive_ptr<Y> const & p) # endif { os << p.get(); return os; } </code> -Ilya