The current observations confirm and extend earlier data demonstrating the deleterious effects of ethanol in the C57BL/6J mouse. Ethanol given to pregnant mice from gestation-day 5 to gestation-day 11 reduced the number of mice going to full term, decreased the number of pups per litter, and lowered the birthweight of the live pups. Prenatal exposure to ethanol also produced a high incidence of hydronephrosis in the offspring.