Pregnant rats were exposed to cigarette smoke and ethanol separately and in combination in order to determine the interactive effects of these two drugs on outcome of pregnancy. The animals were exposed to cigarette smoke daily for a 2-hour period from day 1 to 20 of pregnancy. The ethanol was given in the drinking water in progressively higher concentrations. It was 10% for the first week and 20% during the next three weeks before mating, and 30% from day 1 to 20 of pregnancy. Exposure to cigarette smoke alone significantly reduced fetal weight when compared to pair-fed and ad libitum controls. The combination of ethanol plus smoke caused a significantly greater reduction in fetal weight than did ethanol alone. These findings indicate that prenatal exposure to the combination of alcohol and cigarette smoke exerts a synergistic rather than an additive effect on fetal growth.