The concentrations in plasma of estradiol, estrone, testosterone and 4-androstene-3,17-dione and their monosulphates and glucuronides were determined after oral administration of 0.3 g ethanol per kg body weight to four men. The levels of the unconjugated steroids did not change in a consistent way. In contrast, the concentrations of estradiol monosulphate and estradiol glucuronide increased markedly. The increase paralleled the blood alcohol concentrations and control levels were reached 3 h after the ethanol intake. A coupling of ethanol oxidation with reduction of dehydroepiandrosterone sulphate has previously been established, and it is suggested that the ethanol-induced change of the hepatic redox level affects the interconversion of conjugated forms of estradiol and estrone resulting in elevated levels of conjugated estradiol. This could have a feminizing effect and affect the feed-back regulation of gonadal hormone production.