Plasma oxytocin (OT) levels were measured before and after stimulation with estrogens (1 mg ethynylestradiol orally) or with insulin (0.15 IU/kg)-induced hypoglycemia in seven underweight women with anorexia nervosa, eight normal weight bulimic women, and nine normal controls. Anorectic patients were amenorrhoic; they were tested at their first hospitalization (first tests) and again 8 to 9 weeks later (second tests) when they were eating normally, but were still at a low weight. In addition, anorectic women were tested 16 to 17 weeks after the first test (third tests), when their weight was restored to normal. Normal and bulimic women were tested on the fourth days of normal menstrual cycles. Insulin induced similar hypoglycemic responses in all groups. At each time point of the estrogen tests, plasma estrogen levels were similar in bulimic and normal women, whereas they were significantly lower in anorectic subjects. There were no differences in the basal levels of OT among groups. Both insulin-induced hypoglycemia and estrogen treatment produced striking OT increments in bulimic and control women, without significant differences between groups. During the first tests, no significant increase in plasma OT levels was observed in underweight anorectic women in response to both releasing stimuli. After partial weight recovery, the anorectic women showed a slight, but significant, increase in the OT responses to both insulin-induced hypoglycemia and estrogen administration. Both hypoglycemia- and estrogen-induced OT increases observed during the second tests were significantly lower in underweight anorectic patients than in normal controls. Anorectic subjects regained normal OT responsiveness to both stimuli after complete weight recovery.(ABSTRACT TRUNCATED AT 250 WORDS)