Angiotensin II receptors have been quantitated in single rat adrenal medullas by incubation oftissue sections with r r sl-[Sarr]-AII, autoradiography with exposure to 3H-sensitive Ultrofllm, computerized densitometry and comparison with r25l-labelled standards. Rat adrenal medulla contains a single class of high affinity AII receptors with a ¡<" of0.84 + 0.02 x lOe M rand a B^.,of3259 + 502 fmol/mg protein, one of the highest densities in AII receptors found in rat tissues. These observations provide evidence for a local site ofaction of AII in the release ofadrenal medullary catecholamines.