Hi Jean-Paul, Thanks for the info. Chimera crashes that occur just on specific machines (mac, linux, windows) are almost always graphics driver problems and there is little the Chimera developers can do about those. Some crashes may also be related to loading large volume data sets (totaling > 1 Gbyte) using 32-bit versions of Chimera. There simply isn't enough addressable memory in the 32-bit address space (only 4 Gbytes used by libraries, os, stack, ...). We try to catch large memory allocation failures so they do not cause a crash but many allocations are done by the >30 third-party libraries we use. We plan on making a 64-bit Mac Chimera but it is not ready yet. A 64-bit version is available for Linux. The most common Chimera crash scenario is calculating solvent excluded molecular surfaces (menu entry Actions / Surface / show) which occurs on all platforms (mac, linux, windows) in Chimera production release 1.2470 (Nov 2007) but not in recent snapshots and daily builds. Tom