Abstract Relationships between variations in blood alcohol level (BAL) and blood alcohol level discrimination accuracy were investigated as a function of menstrual cycle, hormonal variations, and behavioral tolerance to alcohol in 20 female social drinkers. All subjects consumed a moderate dose of alcohol on three occasions during one complete menstrual cycle. Subjects estimated their level of intoxication eight times during each drinking session. Each subject's behavioral tolerance to alcohol each session was assessed by a body sway procedure. Subjects also completed detailed questionnaires on symptoms related to menstrual period and familial history of alcohol use. Contrary to earlier reports, (1) no difference in total time of intoxication or in other indices of ethanol metabolism was found between women ( N = 9) who were not taking birth control pills and those ( N = 11) who were and (2) no difference was found in peak BAL as a function of menstrual cycle phase. Stage of menstrual cycle did not affect the accuracy of BAL estimation. A trend approaching significance suggested that, with increasing BAL, women in the oral contraceptive group were more accurate in their estimates of intoxication. A significant interaction between menstrual cycle phase and tolerance levels was found; high tolerant women were significantly less accurate than low tolerant women in estimating BAL during the midcycle phase of the menstrual cycle.