PACAP did not affect secretory activity of dispersed rat adrenocortical cells, but it markedly raised aldosterone (ALDO) and corticosterone (B) production by adrenal slices, containing both medullary and cortical tissues. The secretagogue effects of PACAP were suppressed by PACAP(6-38), a specific competitive antagonist. Isoprenaline (IP) enhanced ALDO, but not B secretion of adrenal slices, and l-alprenolol (AL) completely blocked IP effect. AL and corticotropin-inhibiting peptide (CIP) partially reversed ALDO response to a maximal effective concentration of PACAP; AL did not affect B response to a maximal effective concentration of PACAP, while CIP completely annulled it. Quarters of regenerated adrenocortical autotransplants, that are completely deprived of chromaffin cells, though displaying ALDO and B responses to IP and ACTH, were insensitive to PACAP. The hypothesis is advanced that adrenal medulla plays a pivotal role in the mechanism(s) underlying the adrenocortical secretagogue action of PACAP, being mineralocorticoid and glucocorticoid responses probably mediated by the release by chromaffin cells of catecholamine and ACTH or exclusively ACTH, respectively.