Angiotensin II (AII; 1.0 µl of 10–10M) injected bilaterally into the anterior hypothalamus-preoptic area of the brain produced a 100% increase in mean whole blood LH concentrations in ovariectomized rats treated with estradiol and progesterone. Injections of equal volumes and concentrations of the peptide into the third cerebral ventricle or into the posterior hypothalamus did not affect blood LH values. The effects of AII administration into the rostral hypothalamus were dose-related and specific. Equimolar injections of angiotensin I or angiotensin III into this region did not significantly affect blood LH levels. Taken together, these data demonstrate that the anterior hypothalamus-preoptic area, compared to the third ventricle or more caudal brain sites, is particularly sensitive to the specific stimulatory actions of AII on LH relea