The corticotropin (ACTH) or cholera-toxin-induced cAMP production by cultured bovine adrenal cells increased progressively between days 0 and 7 of culture. Angiotensin II (A-II), which inhibited both basal and ACTH-stimulated adenylate cyclase of crude adrenal membranes, had no effect on ACTH-induced or cholera-toxin-induced cAMP production by fresh isolated cells (day 0) but progressively potentiated the stimulatory action of both effectors from day 0----1 to day 7 of culture. In contrast, phorbol ester had a potentiating effect on fresh isolated cells. Pretreatment of cells with pertussis toxin enhanced the potentiating effect of A-II on cells between 0 and 3 days of culture, but not after 7 days. ADP-ribosylation by cholera toxin (ribosylating alpha s proteins) or pertussis toxin (alpha i proteins), of adrenal membranes prepared from fresh isolated or cultured cells revealed an increase in alpha s and a dramatic decrease in alpha i, the ratios alpha i/alpha s on days 0, 3 and 7 of culture were 4, 0.6 and 0.1 respectively. These results indicate that (a) A-II had a double effect on ACTH-induced or cholera-toxin-induced cAMP production: one inhibitory mediated by Gi, the other stimulatory mediated by protein kinase C activation; this could explain the lack of apparent effect of A-II on fresh cells; (b) the progressive decrease of alpha i might be responsible for the appearance of the potentiating effect of A-II whereas the progressive increase of alpha s could explain the enhanced responsiveness to ACTH or cholera toxin of cultured cells.