The long-term objectives of this research project are to identify and characterize this new peptide in neuronal tissue and to determine its physiological and pharmacological mode of action. This material was originally isolated as an immunoreactive substance that cross-reacted with a physalaemin-specific antiserum; mass spec date gave a mass ion of 866 and amino acid analysis indicated that it was an octapeptide. This peptide is not a tachykinin due to the absence of amino acids that typify that class of bioactive peptides. Preliminary data on its biological activities indicate an increase in tonus and phasic motility of guinea-pig illeal smooth muscle, with slower onset and relaxation than physalaemin. In rabbit large intestine, it appeared to inhibit tone and motility which was reversed by physalaemin. Thus, this peptide may prove to be a prototype of a new class of mammalian peptide hormones.