Chick embryos given a single dose of ethanol (1.0 g/kg) at the start of incubation (day 0) had widely differing levels of blood alcohol when sacrificed on day 7 and the blood alcohol levels were inversely correlated with whole body and brain weight. Clearance of the alcohol by the embryos was inhibited by simultaneous treatment with 4-methyl pyrazole and this treatment potentiated the brain growth inhibition due to ethanol. Treatment with indomethacin lowered blood alcohol levels on day 7 and protected against the growth inhibition. These data suggest that early chick embryos have varying amounts of alcohol dehydrogenase-like metabolic activity and that higher levels of this activity protect against alcohol-induced brain growth inhibition in this model. If similar variations in the ability to metabolize alcohol exist in human fetuses, it may represent a mechanism by which comparable maternal doses of alcohol produce widely varying fetal effects.