Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid peptide of the secretin-vasoactive intestinal peptide (VIP) family. To investigate whether PACAP alters chief cell function, we prepared isolated chief cells (> 90% pure) from guinea pig stomach. PACAP-38, PACAP-27, VIP, and secretin all caused a threefold increase in pepsinogen release. The dose-response curves of PACAP-38, PACAP-27, and VIP were biphasic, whereas with secretin it was not. The first phase comprised 40% of maximal release, and each of the three peptides (PACAP-38, PACAP-27, and VIP) were equipotent (EC50 0.1-0.3 nM). For the second phase, comprising 60% of maximal release, the relative potencies were PACAP-38 > PACAP-27 = VIP. 125I-labeled secretin, 125I-VIP, and 125I-PACAP-27 all demonstrated saturable binding to chief cells. Binding of both 125I-PACAP-27 and 125I-VIP was inhibited completely and with similar potencies by PACAP-38, PACAP-27, and VIP. Secretin had a > 500-fold lower affinity than PACAP-38 for displacing both 125I-PACAP-27 and 125I-VIP. With 125I-secretin, secretin was the most potent, and was 197 times more potent than PACAP-38, which was 6-8 times more potent than both PACAP-27 and VIP. We conclude that both PACAP-38 and PACAP-27 stimulate pepsinogen secretion from dispersed chief cells. In contrast to a number of other tissues, no evidence for a high-affinity receptor that interacted only with PACAP was found. PACAP and VIP interact with equal high affinity with a common receptor and with low affinity with the secretin receptor.