The purpose of this study was to evaluate the detectability of an effect of moderate alcoholic beverage consumption on the biologic correlate of postmenopausal estradiol levels. Total weekly consumption and beverage-specific intake were assessed using both self-reported usual consumption information and prospective food record data. In terms of total weekly drinks, discrepancies were observed in 35 of the 101 women who reported alcohol use; no consistent pattern of overreporting/underreporting was seen. Although the two alcohol estimates were highly correlated, the relationship between estradiol levels and total weekly alcohol intake was found to be detectable when alcohol consumption based on the food record data was analyzed, but not when the self-report data were examined in a two-tailed hypothesis-testing situation. Evaluating the association between postmenopausal estradiol levels and the two estimates of alcohol intake in random samples of varying sample sizes generated from the mother population of 128 normal postmenopausal women confirmed the finding that the prospectively obtained alcohol data better predict the relationship. Based on the results of this study, it must be concluded that self-reported usual alcohol consumption data must be used with caution when examining an association between alcohol intake and a biologic effect.