The number of obstetric patients with polydrug abuse problems has increased substantially in recent years. One of the most common drug combinations is alcohol and cocaine. The effect of this drug combination on pregnancy is, therefore, of interest. Consequently, the present study investigated the relative and interactive effects of these two drugs on pregnancy outcome in an animal model. Alcohol and cocaine were administered, both separately and in combination, to separate groups of pregnant Long-Evans rats from gestation day 7-19. Animals were then sacrificed and examined on gestation day 20. Control animals were given vehicle only or were nontreated. The isobolographic method was used to evaluate the effects of the alcohol-by-cocaine interaction on select maternal and fetal variables. This method of analysis indicated that alcohol and cocaine had interactive effects that were linearly additive for some variables and infraadditive for others. In general, the results suggest that the alcohol-plus-cocaine drug combination poses a greater risk to pregnancy than either drug alone.