An episodic secretion of LHRH in pituitary portal blood was observed in ovariectomized and hypophysectomized rats under Saffan anesthesia. This anesthetic did not effect the pulsatile release of LH in ovariectomized rats. Third-ventricular administration of an LHRH agonist, at a concentration which did not cross-react in the LHRH RIA, suppressed both the pulse amplitude and frequency of LHRH release. This inhibitory action of the LHRH agonist on LHRH release was blocked by an LHRH antagonist.