SummaryThe acute response to simulated hypoglycemia induced by 2- deoxyglucose (2DG) was compared with the prolonged fasting test as a possible screening test for detection of childhood hypoglycemia. Ten children, ages 2-9 yr, without a documented history of hypoglycemia were classified retrospectively as reference subjects. While fasting, their plasma glucose decreased to an average of 50 mg/dl (range, 30-74) between 28-36 h. After infusion of 2DG, 50 mg/kg IV over 30 min, their plasma glucose increased by an average of 35 mg/dl (range, 19-56) between 60- 120 min. The half-life of plasma 2DG was 48 min. Twenty-three other children in the same age range had an abnormal response to one or both of these tests. Thirteen of these children became definitely hypoglycemic while fasting (glucose<30 mg/dl) and also failed to increase their plasma glucose by more than 10 mg/dl after 2DG. Five children had plasma glucose values between 30-40 mg/dl during the first 24 h of fasting that were associated with a change in mental status but responded to 2DG with an increase in plasma glucose. The remaining five subjects had an apparently normal response to fasting but did not respond to 2DG; two of these had documented spontaneous hypoglycemia. No cases of documented hypoglycemia were undetected by either test. It is concluded that the 2DG test is a short safe supplement to fasting which is equally effective as the prolonged fasting test in detecting hypoglycemia. Neither test alone is completely reliable, but the combination is complementary.