Hi Jane, Are you building R from source on your Mac or using the R.app binary? I use OS X and build R from source and was able to build graphviz 2.2.1 from source on the mac and this does work with Rgraphviz. That said, it may be difficult to find the 2.2.1 source package and I don't know whether or not the latest graphviz release is easy to build on OS X. I have built it on Linux and encountered some challenges. + seth