In order to investigate the responses of insulin and glucagon to the same glycemic stimulus in late normal pregnancy and post partum, appropriate quantities of glucose were infused intravenously in 7 normal women at both stages. In this manner similar glucose curves were obtained in the 2 conditions. The insulin response to glucose infusion was increased 3.8 times in late pregnancy, whereas the suppression of glucagon was similar in late pregnancy and post partum. The results confirm that the β-cell sensitivity to a glycemic stimulus is substantially increased in normal late pregnancy, but the α-cell sensitivity to a glycemic stimulus is unaffected by pregnancy.