LHRH was administered by continuous 4-hour intravenous infusion to 14 anorexia nervosa patients on a refeeding programme. Infusions were repeated in 7 patients following weight gain and in 4 after a course of bromocriptine. Five healthy female volunteers in the early or mid-follicular phase of the menstrual cycle served as controls. The LH response was diminished in patients at 65% standard weight, but was of progressively increasing magnitude in patients at 80% and 95% standard weight. The pattern of LH response to the 4-hour infusion was suggestive of a deficient stimulation by endogenous LHRH in patients at extremely low weights, and of an impaired oestrogen feedback mechanism in patients at intermediate weights. Bromocriptine enhanced the LH response on one occasion in patient with moderately elevated plasma HPR values, but failed to produce a similar effect when given to 3 patients with normal HPR levels. The mean FSH response did not differ significantly between patients in different weight categories, although those at 65% standard weight had a markedly greater variance of response. Plasma oestradiol values were lower in patients at 65% standard weight than in those at higher weights.