Serum thyrotropin (TSH), prolactin (PRL), and growth hormone (GH) levels were measured before and after stimulation with thyrotropin-releasing hormone (TRH) in 10 patients with bulimia, 7 with features of the restricting subtype of anorexia nervosa, and 6 with bulimic subtype of anorexia nervosa. The mean basal levels of TSH, PRL, and GH did not differ among the three groups. A delayed TSH response was found in 86% of the restricting anorectics, 80% of the bulimic anorectics, and 22% of the bulimics. The PRL response was normal in all patients, with no significant difference among the three groups. Elevated basal GH levels were found in 29% of the restricting anorectics, 33% of the bulimic anorectics, and 33% of the bulimics. An abnormal GH increase after TRH stimulation was observed in 50% of the restricting anorectics, 20% of the bulimic anorectics, and 13% of the bulimics. These results suggest that some patients with bulimia, and some with anorexia nervosa, have a hypothalamic dysfunction. These neuroendocrine abnormalities do not appear to be due solely to low weight or to metabolic changes resulting from binge eating and are not associated with depressive symptoms.