Hi Hugues, I've checked in a fix to CVS. Sorry, but this fix won't make it into the imminent release of boost 1.31.0. Anyways, your program now gives the following output: After initializing properties for G1: Global and local properties for vertex G0[C]... G0[C]= A1 G1[A1]= A1 Global and local properties for vertex G0[E]... G0[E]= B1 G1[B1]= B1 Global and local properties for vertex G0[F]... G0[F]= C1 G1[C1]= C1 After initializing properties for G2: Global and local properties for vertex G0[A] G0[A]= A2 G2[A2]= A2 Global and local properties for vertex G0[C]... G0[C]= B2 G1[A1]= B2 G2[B2]= B2 Cheers, Jeremy P.S. The subgraph class was a late addition to the graph library and it is a fairly complicated class that was not well tested. I would not be surprised if there are more bugs. _______________________________________________ Jeremy Siek <jsiek@osl.iu.edu> http://www.osl.iu.edu.edu/~jsiek Ph.D. Student, Indiana University Bloomington C++ Booster (http://www.boost.org) Office phone: (812) 856-1820 _______________________________________________