Intravenous glucose tolerance tests were performed on 232 randomly selected, pregnant subjects and 149 of the same women post partum. To analyze the data from these tests, new criteria were established to determine which glucose values to include in calculating the rate of disappearance of glucose, the k rate. Intravenous glucose tolerance was significantly impaired in pregnancy, compared to post partum, when judged by k rates or simply by the smaller proportion of persons whose gestational blood sugars returned to fasting levels before 60 min.