Hi Geoff, Chimera freezes up for me after I open diamond.pdb and then try to show it as ball and stick or sphere. It doesn't freeze up with wire display style. When it freezes I use: % ps -xwww | grep python2.2 3676 ?? R 0:44.37 /Users/goddard/Applications/Chimera-X11-1700.app/Contents/Resources/bin/python2.2 /Users/goddard/Applications/Chimera-X11-1700.app/Contents/Resources/share/__main__.pyp % kill 3676 The Chimera executable is python2.2 and this just kills Chimera, not the X server. It doesn't appear in the Force Quit dialog because it is not a native Aqua windows application. Are you using Chimera build 1700 (March 27, 2003)? The Chimera Help/Version Info menu entry will tell you which version you have. I'll look into why Chimera 1700 is freezing on diamond.pdb. Tom