The present study was designed to compare the relative validity of the 2-hour postprandial glucose test (2hpp) and the rapid intravenous glucose tolerance test (IVGTT) as predictors of the outcome of pregnancy. Both tests were performed at the onset of the third trimester of pregnancy in each of 77 women who constituted a selected group of patients considered to be at high risk of developing gestational diabetes. Data concerning newborns were recorded in each case. The IVGTT was found to give a significantly larger yield of positive results (44.15%) as compared to the 2hpp test (35.06%). Furthermore, significantly heavier babies and higher rates of perinatal morbidity were noted in those cases with abnormal IVGTT results as compared to those with normal values. No such association was seen in those cases with abnormal values of 2hpp. These results suggest that the rapid IVGTT is a more dependable test than a single postprandial blood glucose estimation in screening pregnant women for gestational diabetes.