Antibodies to the molluscan neuropeptide, Phe-Met-Arg-Phe-NH2 (FMRFamide) react with material in extracts of chicken brain. One of the immunoreactive peptides has the sequence Leu-Pro-Leu-Arg-Phe-NH2 (LPLRFamide). We have now raised antibodies to LPLRFamide and used these to examine the distribution and molecular forms of LPLRFamide-like peptides in the chicken. Several forms can be distinguished on the basis of HPLC retention times. Concentrations are highest (200 pmol X g-1) in hypothalamus, and lowest (less than 10 pmol X g-1) in cerebellum, spinal cord and gut. There are two common residues in FMRFamide and gastrin/CCK related peptides (-Met-X-Phe-amide). However, LPLRFamide is readily distinguishable from avian CCK and gastrin. The latter, like the mammalian gastrins, is a relatively strong stimulant of acid, and a weak stimulant of pancreatic enzyme secretion, in the chicken. The physiological roles of the vertebrate peptides with FMRFamide and LPLRFamide immunoreactivity remain to be elucidated, although evidence is emerging to suggest that they might act as transmitters in CNS regions associated with the input of sensory information (dorsal spinal cord and nucleus tractus solitarius).