The role of AII receptors subtypes, AT1 and AT2, in the regulation of aldosterone secretion was studied in adrenal glomerulosa cells and membranes from rats on normal and low sodium intake, using AII receptor subtype-specific antagonists. In adrenal glomerulosa cells, more than 90% of the receptors were AT1 and there was a good correlation between the potencies of the antagonists to inhibit ligand binding, and AII-stimulated aldosterone production and inositol phosphate formation. The inhibition of basal and ACTH-stimulated cAMP by AII was also abolished by the AT1, but not the AT2, antagonist. Sodium restriction for 6 days increased both receptor subtypes in the same proportion, but only the AT1 antagonist inhibited AII-stimulated aldosterone production. The data demonstrate that AT1 receptor mediates the regulatory actions of AII in the adrenal zona glomerulosa.