When debugging C or Fortran code in R, it's helpful to run R under a debugger. I use Insight, which is a wrapper for gdb. One problem is that in Windows hitting break doesn't cause a trap to gdb, so it can be hard to stop the process. I've added a menu item to the r-devel version of Rgui (Misc|Break to debugger) which triggers a trap to the external debugger. Unfortunately, choosing this menu item crashes R if you're *not* running under a debugger, so I haven't made it easy to see: you need to compile src/gnuwin32/rui.c with DEBUG=T in order to get it. If anyone knows of code that traps to a debugger when one is present, and is safely run when one is not, please let me know. Duncan Murdoch