In order to clarify the role played by pancreatic alpha-cell dysfunction in the impaired glucose recovery from hypoglycemia in patients with anorexia nervosa, the response of pancreatic alpha-cells to insulin-induced hypoglycemia was investigated in 16 patients with anorexia nervosa before and after treatment. The results were compared with those obtained after loading with arginine. Before treatment, despite comparable falls in plasma glucose levels, glucagon secretion was significantly reduced in the anorectic patients compared with control subjects. In addition, glucose recovery from hypoglycemia in the patients was attenuated. However, after treatment, both glucagon secretory activity and plasma glucose recovery following insulin-induced hypoglycemia were restored to normal. Plasma glucagon responses to arginine infusion were not significantly different in the untreated anorectic patients and control subjects. However, the plasma insulin response in the patients was significantly lower than in the control group. These results suggest that the impaired recovery of plasma glucose levels from insulin-induced hypoglycemia in patients with anorexia nervosa is primarily attributable to impaired pancreatic alpha-secretory capability. In addition, this abnormality in pancreatic alpha-cell function is reversible with treatment leading to improved nutrition and weight gain.