Hi Grant, I fixed the Chimera problem that prevented it from starting on Mac OS 10.4 (Tiger). It was an incompatibility between the JPEG and TIFF libraries included with Chimera and the Mac system libraries. The fix is in the Chimera 1.2120 snapshot on the download page. http://www.cgl.ucsf.edu/chimera/download.html Unfortunately the fixed Chimera turns up other problems on Tiger. With my ATI Radeon 9800 Pro graphics card Chimera crashes when a ribbon is displayed for a molecule. This appears to be a graphics driver bug in Tiger. Also molecular surfaces disappear when they are rotated. This appears to be another driver bug. These problems do not occur on Mac OS 10.3 or on other platforms (Linux, Windows, SGI), nor do they occur with Radeon 9800 graphics on Windows. We will be submitting bug reports to Apple, but the soonest possible fix will be when Mac OS 10.4.1 comes out. These problems may not occur with other graphics cards, for example, Nvidia cards. If you try Chimera 1.2120 with another graphics card we would like to hear how it works (good or bad). Tom