A prospective study was undertaken to investigate the carbohydrate and lipid metabolic effects of the oral contraceptive nurethindrone. An oral glucose tolerance test was performed before and 1 year after the daily oral administration of 0.35 mg of norethindrome to 31 women. Measurements were made of glucose, insulin, cholesterol, and triglycerides. During the year there was no significant weight change in the women, and the fasting cholesterol values were unaffected by the steroid. The fasting triglycerides decreased as normally occurs in the late postpartum period. There was no change in the blood glucose curve, hut there was a statistically significant elevation produced in all of the plasma insulin values. These data suggest that this 19-nor progestogen steroid can affect the peripheral activity of insulin and thus require higher blood levels in order to obtain the same glucose homeostasis.