Hi Charlie, You will need the Mac Python configuration header file pyconfig.h to compile your Python module on the Mac and have it work with Chimera. I added Chimera and third party header files for the Mac to our source code download page: http://www.cgl.ucsf.edu/chimera/sourcecode.html Compiling a python module on the Mac also involves some special linking flags. The Mac has "dynamic libraries" and "bundles" and as far as I know Python can only import bundles. That was the case a few years ago. Here are a couple link examples that make bundles on the Mac. gcc -I/usr/local/src/staff/goddard/mac-10.4/build/include -L/usr/local/src/staff/goddard/mac-10.4/build/lib -DUSE_DYLD_GLOBAL_NAMESPACE -bundle -bundle_loader /usr/local/src/staff/goddard/mac-10.4/foreign/Python-2.4/bin/python2.4 Scientific_netcdf.o -Lnetcdf/lib -lnetcdf -o Scientific_netcdf.so cc -bundle -bundle_loader /usr/local/src/staff/goddard/builds/mac-10.3/chimera-2095/build/bin/python2.4 -o _contour.so -O -Wall -Wno-long-double contourdata.o pycontour.o _contour.o ContourObject.o -L/usr/local/src/staff/goddard/builds/mac-10.3/chimera-2095/build/lib -L../_volumearray -lrcarray -lwrappy -lstdc++ The flags -bundle and -bundle_loader <path-to-python-executable> are the important ones. These replace the usual -shared on other platforms. I'm not sure about -DUSE_DYLD_GLOBAL_NAMESPACE -- we don't use that for building the python modules we write but it appears that third-party packages we use define that macro. Tom