21 women (mean age 60 years, range 48–72) were given depot medroxyprogesterone acetate (DMPA), 1,000 mg/week parenterally for 6 months, as part of the treatment for endometrial carcinoma in either clinical stage I or II. Before treatment and after 1, 3 and 6 months of treatment serum apolipoprotein AI was analyzed by electroimmunoassay. There was a significant decrease in apolipoprotein AI after the administration of DMPA, compared to the value before treatment. A low level of apolipoprotein AI is considered a risk factor for the development of atherosclerosis and cardiovascular disease. Such a risk might therefore be anticipated if the period of treatment was extended to several years.