Because alcoholism has adverse effects on zinc nutrition and many pregnant women consume less than the recommended dietary allowances of zinc, we postulated that zinc deficiency acts as a co-teratogen with alcohol in the fetal alcohol syndrome. We compared the effects of alcohol on progeny of pregnant mice fed a zinc-deficient diet compared to those fed a diet with adequate zinc. Pregnant CBA mice (n = 66) were fed the Lieber-DeCarli liquid diet with 0, 15, or 20% ethanol-derived calories containing 0.3 (low) or 8.5 (high) micrograms zinc/ml. Dams were sacrificed on day 18 of gestation. Resorptions, malformations, and individual fetal weights were recorded. Analysis of fetuses included assays for zinc, assessment of soft tissue malformations, and alizarin red staining for skeletal malformations. Fetal weights were lower in the groups fed the zinc-deficient diet for each concentration of alcohol (p less than 0.005). The groups fed the combination of low zinc plus alcohol had 37-52% resorptions, while the animals on the zinc-deficient diet without alcohol or the high zinc diet with alcohol had 0-2% resorptions. Skeletal malformations were related to alcohol concentration but not zinc intake, while external malformations were higher in those maintained on the low zinc-ethanol diet. These results suggest that zinc deficiency potentiated the teratogenic effects of alcohol and that nutritional intervention for alcoholic women during pregnancy might reduce the incidence or severity of fetal alcohol syndrome.