Plasma concentrations of ethynyl estradiol and norethindrone [used in hormonal contraceptives] in women were measured by radioimmunoassays after oral administration of 50 .mu.g and 1000 .mu.g, respectively. The maximum values were obtained 1 h after administration. The calculated half-life was 61/2 h for ethynyl estradiol and 7 h for norethindrone. At most 2-3% of the administered dose was present in the plasma at 1 h and had decreased to about 0.5% by 24 h.