Evidence is accumulating that the adrenal medulla exerts a paracrine control on the secretory activity of the cortex by releasing catecholamines and several regulatory peptides. Pituitary adenylate-cyclase activating peptide (PACAP) is contained in the adrenal medulla of several mammalian species and in human pheochromocytomas. Thus, we investigated whether PACAP exerts a modulatory action on steroid secretion by the human adrenal cortex in vitro. Adrenal slices (including both capsule and medulla) and dispersed adrenocortical cells (obtained from the gland tail deprived of medulla) were employed. Both adrenal preparations secreted aldosterone (ALDO) and cortisol in response to 10 nmol/L ACTH. PACAP (10 nmol/L) was found to enhance basal ALDO production by adrenal slices, but not by dispersed cells. PACAP was ineffective on cortisol secretion of both preparations. Adrenal slices displayed a marked ALDO, but not cortisol, secretory response to 100 nmol/L isoprenaline or noradrenaline. l-Alprenolol (1 mumol/L), a specific beta-adrenoceptor antagonist, completely suppressed the ALDO response to both beta-adrenoceptor agonists and 10 nmol/L PACAP, without per se altering basal ALDO output by adrenal slices. PACAP (10 nmol/L) induced a net rise in catecholamine release by adrenal slices. Taken together, our present findings suggest that PACAP indirectly stimulates ALDO secretion by the human adrenal cortex, probably by eliciting the local release of catecholamines by medullary chromaffin cells that are also scattered in the cortical tissue, especially the zona glomerulosa.