I've made a change in the 1.5 build that could affect script/extension writers that use the StructureSequence.residues list. That list can now contain None values. This is because now the sequence is the full sequence if available in SEQRES records even if some of the corresponding structure is missing. Such missing structure has None for the Residue value. --Eric Eric Pettersen UCSF Computer Graphics Lab http://www.cgl.ucsf.edu