1. Having previously isolated helodermin, the major peptide like vasoactive-intestinal-peptide and peptidehistidine-isoleucinamide, from the venom of the lizard Heloderma suspecturn, we decided on a systematic exploration of all (VIP-PHI)-like peptides present in the venom of another lizard of the Helodermatidae family: Heloderma horridurn.2. Six (VIP-PHI)-like peptides (PHHI to 6) were purified to homogeneity from the venom of the lizard H . horridurn with PHH3 and PHH4 representing two minor forms. All peptides cross-reacted in radioimmunoassays for helodermin and PHI but not for VIP. They yielded four fragments (T1 to T4) after trypsin digestion. T1, T2 and T3 showed the same retention time by reverse-phase HPLC and the same amino acid composition; the differences were confined to T4, the C-terminal sequence. PHH5 and PHH6 were found to be identical to synthetic helospectins I and I1 respectively. PHHl and PHH3 probably resulted from a secondary modification of PHHS, while PHH2 and PHH4 derived from PHH6. Thus, the VIP-like peptides, previously called helospectins, are in fact typical of H . horridum venom.3. We confirmed that helodermin is the major (VIP-PHI)-like peptide of the venom of H . suspecturn and observed its absence in H . horridurn venom. Also, we found that positions 8 and 9 of helodermin are occupied by two Glu residues instead of two Gln as previously published. Helospectin-like material was also present in H . suspecturn venom but in very small amount.4. In both venoms all VIP-like peptides were equally potent and efficient when tested for (a) their ability to occupy VIP as well as secretin receptors in rat pancreatic membranes and VIP receptors in rat liver membranes, and (b) the ensuing activation of adenylate cyclase in both membrane preparations.In 1982 Raufman et al. 111 described the presence, in the found that the active material in the venom stimulated rat venom of the lizard Heloderma suspectum (also called Gila monster), of a biologically active material closely related to vasoactive intestinal peptide (VIP), as it inhibited 1251-VIP binding, stimulated cyclic AMP production and promoted amylase secretion in dispersed guinea-pig pancreatic acini. In 1983 similar observations were made by Amiranoff et al. [2] using isolated intestinal glands as a target system, and by ourselves on rat pancreatic plasma membranes [3]. We also