A prospective study to investigate the metabolic effects of the progestogen ethynodiol diacetate (ED) was conducted on 71 women (mean age 23.3 years mean parity 2.0) receiving a daily dose of .25 mg of ED. Blood levels of glucose insulin and growth hormone analyzed by radioimmunoassay techniques were measured during a 3-hour oral glucose tolerance test performed before steroid initiation and after 6 months of use. While ambulatory fasting growth hormone levels did not change there were significant elevations of both glucose and insulin levels. In addition there was a deterioration in the glucose tolerance curves of 12.9% of the "normal" subjects. A positive and significant association was found between elevations of glucose and insulin levels and women of older age those obese at treatment initiation and those gaining excessive weight while on therapy. The importance of considering the metabolic effects of the progestogen component of oral contraceptives is stressed.