Hi Grant, Chimera comes with Tcl/Tk and Python and everything that is needed. Either your Chimera installation did not work, or environment variables are tripping up Chimera. To see if all of Chimera got installed use Mac Finder and single click on Chimera. On my Mac OS 10.3.4 system it says 132.9 Mb disk space is being used by Chimera. Is that what you see? More likely the problem is with environment variables. Do you have PYTHONHOME set in your environment? If you start a Terminal and type echo $PYTHONHOME it will say if this variable is set. Other environment variables that could mess up Chimera are PYTHONPATH and CHIMERA. If all of this looks ok try % ls /Applications/Science/Chimera-1.1951.app/Contents/Resources/share/Lighting from a Mac Terminal. This is the location of the missing file referenced by the Python error you sent. You should see the following files: ChimeraExtension.py* controller.py* __init__.py* ChimeraExtension.pyc controller.pyc __init__.pyc Lastly, we have separate Mac OS 10.2 and 10.3 versions of Chimera on our web site. If you still have the Chimera dmg it should be chimera-1.1951-osx10_3_x11.dmg, not chimera-1.1951-osx_x11.dmg. Tom