Increased incidence of myocardial infarction, arteriosclerosis and hypertension in oral contraceptive steroids users has been recognized as serious problem. Evidence have been accumulated that oral contraceptive steroids cause an increase in serum lipid levels, mainly triglyceride as well as an increase in serum cholesterol concentration in some women. Effect of oral contraceptives on serum lipids have been predominantly confirmed in Europian and American women. It should be emphasized that effects of contraceptives may he influenced by differences in nutrition, climate, socioeconomic status and race. The present study was, therefore, attempted to determine the effect of oral contraceptive steroids on serum lipid levels in Korean women and also to demonstrate whether the duration of pill treatment may affect serum lipid levels. Ten women, who had never taken contraceptive steroids, served as a control. One hundred women on combined oral contraceptive steroids were grouped according to the duration of pill use: duration of less than one year(14 women), 1-2 years(12 women), 2-5 years(29 women), 5-10 years(33 women) and more than 10 years(13 women). Serum levels of cholesterol, phosholipid and triglyceride were measured by enzymatic method, Fiske-SubbaRow method and Sugiura method respectively. The results obtained are as follows; 1) Oral contraceptive steroids increased serum cholesterol concentration by 4.8% as compared with cholesterol value of control group. But this increase was not statistically significant. 2) As compared with control value, concentration of serum phospholipid in pill-treated women decreased by 14.3%, which was statistically significant (p<0.05). 3) Concentration of serum triglyceride in pill-treated women increased by 10.6% over control value, but this increase was not statistically significant. 4) Duration of pill-treatment did not affect serum concentrations of cholesterol, phospholipid and triglyceride. From the results mentioned above, it may be concluded that combined oral contraceptive steroids, at least used for subjects involved in this study, decreased serum phospholipid significantly, thereby influencing serum lipid concentration.