Hi, According to the mpl docs, defining above macro to e.g. 30 should make boost::mpl::list<> take 30 template arguments, and thus enable boost::variant<> to hold 21 different types (default: 20 on my platform (gcc 4.0)). Yet compiling the attached sample program gives me attached error message, which indicates that mpl::list<> still takes only 20 template parameters. Bug? Thanks, Marc -- Marc Mutz -- marc@klaralvdalens-datakonsult.se, mutz@kde.org Klarälvdalens Datakonsult AB, Platform-independent software solutions