Reactive hypoglycemia is being diagnosed with increasing frequency. We compared plasma glucose, insulin, glucagon, epinephrine, and norepinephrine responses to an oral glucose tolerance test and to a mixed meal containing equivalent carbohydrate in 33 patients who had been referred to our institution with a presumed diagnosis of reactive hypoglycemia and in 2 patients who had insulinomas. In addition, a control group of 36 normal volunteers underwent the meal study. During the meal studies, electroencephalograms were obtained. Despite provocation of hypoglycemia by the oral glucose tolerance test, no consistent relationship between hypoglycemia and symptoms was observed. Despite similar symptoms, hypoglycemia did not develop after the meal test in the 33 patients without insulinomas. Both patients with insulinoma became hypoglycemic after ingestion of the meal. When a physiologic stimulus such as a meal is used to duplicate the daily dietary experience of patients, reactive hypoglycemia in the absence of a pancreatic pathologic lesion is an uncommon occurrence.