These proceedings of the Twelfth American Peptide Symposium include 363 articles which were selected for publication on the basis of originality, timeliness and scientific significance. This volume includes contributions on ppetide hormones, neuropeptides, lipid-interactive peptides, peptide and protein conformation, de novo design, structure-activity relationships, synthetic methods, large-scale peptide synthesis, viruses and vaccines, peptide mimetics, peptide inhibitors, immunology and new biologically active peptides.