I don't know how RASMOL determines SSbonds, but my program undertaker finds 6 disulfides in 1aol: SS bond: 2.01426 Ang (1aol)C178.SG and (1aol)C184.SG SS bond: 2.0387 Ang (1aol)C133.SG and (1aol)C146.SG SS bond: 2.01986 Ang (1aol)C121.SG and (1aol)C141.SG SS bond: 2.02242 Ang (1aol)C46.SG and (1aol)C98.SG SS bond: 2.02107 Ang (1aol)C72.SG and (1aol)C87.SG SS bond: 2.04136 Ang (1aol)C73.SG and (1aol)C83.SG I'm using a simple SG-SG distance to detect these disulfides, and I suspect that RASMOL uses a similar mechanism. The 1aol file does not have crystallographer-provided SSBOND or HBOND records, just the HELIX and SHEET records. ------------------------------------------------------------ Kevin Karplus karplus at soe.ucsc.edu http://www.soe.ucsc.edu/~karplus Professor of Biomolecular Engineering, University of California, Santa Cruz Undergraduate and Graduate Director, Bioinformatics (Senior member, IEEE) (Board of Directors & Chair of Education Committee, ISCB) life member (LAB, Adventure Cycling, American Youth Hostels) Effective Cycling Instructor #218-ck (lapsed) Affiliations for identification only.