Twenty-six patients with symptoms suggestive of postprandial hypoglycemia were investigated by oral glucose tolerance test (OGTT). During the OGTT, symptomatic hypoglycemia occurred in 10 (38.5%). Nine of these 10 sugjects were given mixed meal tolerance tests (MMTT) and symptomatic hypoglycemia failed to occur in any case. During the OGTT the nadir glucose was significantly lower than that during MMTT (44.1 +/- 1.5 vs. 77.3 +/- 4.8 mg/dl +/- SEM, respectively; p less than 0.0005). Serum insulin during MMTT peaked significantly earlier than during OGTT (46.7 +/- 7.3 vs. 86.7 +/- 11.7 minutes (SEM, respectively; p less than 0.0125). The early secretion of insulin during MMTT may explain the lack of symptomatic hypoglycemia in these patients. We conclude that reactive hypoglycemia, when tested by a more natural stimulus (such as mixed meal) rather than by OGTT, is uncommon.