The microscopic localization of angiotensin II receptors in the rat brainstem has been accomplished utilizing in vitro receptor autoradiographic techniques. These receptors are highly localized to discrete nuclear regions of the brainstem. Significant densities of autoradiographic grains, indicating the presence of specifically bound [125I]-angiotensin II, were observed in regions of the film corresponding to the nucleus of the solitary tract, dorsal motor nucleus of the vagus nerve, nucleus intercalatus, nucleus commissuralis, substantia gelatinosa of the trigeminal nerve and the inferior olivary nucleus. Previous immunohistochemical studies have indicated the presence of immunoreactive angiotensin II in several of these regions, especially those concerned with central cardiovascular regulatory mechanisms. These results provide additional evidence in support of the hypothesized role of angiotensin II as a central neuromodulator in the regulation of systemic blood pressure.