There used to be a WHAT IF web interface in which a user could submit a PDB ID number and get back an "hadded.pdb" file with hydrogen atoms added. This site no longer exists, and the WHAT IF software is now only available to those who purchase it for 500 Euros (at http://swift.cmbi.kun.nl/whatif/). Is there any other free software or server which can add hydrogens to a PDB file? Jeff Cohlberg -- Jeffrey A. Cohlberg, Professor Department of Chemistry and Biochemistry California State University, Long Beach 1250 Bellflower Blvd. Long Beach, CA 90840 phone (562) 985-4944 fax (775) 248-1263