In vitro responsiveness to various stimulators of aldosterone secretion was studied in a perifusion system using slices obtained from three aldosteroneproducing adenomas (APAs), three adjacent nontumorous glands and three normal adrenal glands. All three APA tissues responded to angiotensin II, K and ACTH in vitro. Angiotensin II (10nM), K (12mM) and ACTH (10nM) cause d more than a 2-fold increase in aldosterone secretion. The sensitivity of APA tissues to angiotensin II was identical to that in normal adrenal cortex. In slices obtained from APA, angiotensin II induced rapid increases in [3H] inositol and [45Ca] efflux, both of which preceded the aldosterone response. These results suggest that APA cells have an almost normal transducing system to stimulators of aldosterone secretion.