In normal subjects, the continuous infusion of calcium during an oral glucose tolerance test (OGTT) did not improve both glucose tolerance and insulin secretion. In diabetics, an improvement in OGTT was observed. The aim of this study was to evaluate the effect of calcium on reactive hypoglycemia. Nine normal controls and fourteen non obese, non diabetic patients with reactive hypoglycemia plasma glucose, less than 2.8 mmol/l during 5 hours OGTT, 75 g glucose, were studied. The protocal included two five hours OGTT with an interval of eight days, with a randomized infusion of normal saline or calcium (35 mEq/5h). An highly significant increase in plasma calcium was observed throughout the calcium infusion, in all subjects. In normal subjects, this infusion did not affect insulin secretion and OGTT, contrary to all patients with reactive hypoglycemia in whom calcium infusion produced significant increase in plasma glucose with p less than 0.05, p less than 0.02 at 120, p less than 0.01 at 180 min. Simultaneously the symptoms of hypoglycemia disappeared. Continuous infusion of calcium suppressed reactive hypoglycemia.