Serum levels of ethinylestradiol (E2) and levonorgestrel (LNG) have been determined in 10 volunteers of similar age after administration of 1 tablet of the oral contraceptives Gravistat and Ediwal, respectively, each containing 0.05 mg E2 and 0.125 mg LNG, using a cross over design. The studies were carried out at intervals of 4 weeks, within the follicular phase of the menstrual cycle and under standardized conditions. Wide variations were observed between the women in the calculated pharmacokinetic parameters, while there was a relatively close correspondence between the intra-individually obtained values, except for one case.