Blood sugar determinations were made four times daily on non-diabetic pregnant and non-pregnant women admitted to hospital for reasons not supposed to influence carbohydrate metabolism. All blood sugar values were found to decrease during pregnancy. The fasting blood sugar decreased from 78 to 65 mg%, and the daily mean value from 99 to 80 mg%. The increase in blood sugar after the main meal of the day was found to be smallest in late pregnancy. The results indicate a progressive change in carbohydrate tolerance during pregnancy. Some implications of the results on the management and outcome of diabetic pregnancy are discussed.