Sex differences in rates of ethanol elimination were investigated in natural siblings to reduce genetic variability as compared to subjects chosen at random. Ethanol was infused intravenously in a dose of 0.6 g/kg of body weight over 45 to 60 min and serial blood samples obtained for 5 hr. The mean rate of ethanol elimination was higher in seven women, not different in one, and lower in one compared with their male siblings. The mean rate of ethanol elimination for all nine women was higher at 1.93 ± 0.12 as compared with the value of 1.69 ± 0.17 mmoles/kg body weight/hr in the men (p < 0.05). Higher rates of ethanol metabolism in women as compared to men may be important in the increased susceptibility of women to liver injury caused by alcohol consumption.