Although the absence of pituitary response to the luteinizing hormone releasing hormone (LHRH) test has been considered proof of a lesion primarily localized at the pituitary level, the possibility exists that an absent pituitary response may represent only the effect of a chronic deficiency of hypothalamic secretion. To verify this hypothesis, 4 patients with primary amenorrhea, hypogonadotropic hypogonadism, and deficient or absent responses to a 25 mug LHRH rapid IV test were treated with 400 mug LHRH infused in 7 hours during each of 3 successive days. The finding that patients with deficient LH responses to a rapid LHRH test became normally responsive to a second equivalent test after a slow and prolonged treatment with the decapeptide suggests that, in these patients, besides a lesion at the pituitary level, a primary defect at the hypothalamic or higher centers may also be suspected.