Dear Dr. Molnar, All chains present in structures open in Chimera should be listed. If two chains have the same ID, however, they will not have separate listings in Select/Chain. Another thing that might be confusing is that residues can be assigned to chains named "het" or "water": Any HETATM residue that does not already have a chain identifier is assigned to chain HET, unless the residue is named WAT or HOH, in which case it is assigned to chain WATER. Additional possibilities are a bug or something strange with the input files. If you have some input files that demonstrate the problem (and don't mind sharing them), you could send them to me or to chimera-bugs@cgl.ucsf.edu along with a short explanation of how to duplicate the problem (how files were opened, what order). Best, Elaine ------------- Elaine C. Meng, Ph.D. meng@cgl.ucsf.edu Computer Graphics Lab and Babbitt Lab Department of Pharmaceutical Chemistry University of California, San Francisco