Proteins (total, albumin, globulin and their subfractions), carbohydrate (intravenous glucose tolerance test), lipids (serum cholesterol, triglycerides and phospholipids), and liver function tests (alkaline phosphatase, lactic dehydrogenase and aspartate aminotransferase activities in the serum, bromsulphathalein retention test and serum bilirubin) were studied in 12 non-lactating healthy Thai subjects before, and subsequently at 3 weeks and 3, 6, 9 and 12 months after the initiation of treatment with injectable medroxyprogesterone acetate (150 mg I.M. every 90 days). Serum protein and lipid levels, and the results of liver function and I.V. glucose tolerance tests, remained unchanged in all subjects throughout the one-year study period. However, a significant and persistent increased insulin level was noted in all subjects, after initiation of the hormone treatment, during the first thirty minutes of intravenous glucose load. It is concluded that injectable medroxyprogesterone acetate used as a contraceptive agent does not interfere with glucose tolerance, lipid and protein metabolism, and that the liver function remains normal during its administration.