Hello, Martin! Graphs are supposed to be passed by reference to visitor functions. Your program didn't do that, so it created tons of temporary graph copies. Changing template<typename V, typename G> void operator()(V v, G g) { ++dummy; } to template<typename V, typename G> void operator()(V v, G& g) { ++dummy; } and template<typename V, typename G> void examine_vertex(V v, G g) { ++dummy; } to template<typename V, typename G> void examine_vertex(V v, G& g) { ++dummy; } should reduce your running times about 500-fold, down to the expected running times. HTH Cromwell Enage __________________________________ Do you Yahoo!? Yahoo! Movies - Buy advance tickets for 'Shrek 2' http://movies.yahoo.com/showtimes/movie?mid=1808405861