The development of two forebrain fiber tracts, the corpus callosum and anterior commissure was examined in BALB/cCF and C57BL/6J mice in relation to moderate maternal consumption of ethanol during gestation. Pregnant animals were fed ethanol 10% v/v in the drinking water from days 5 to 19 of gestation, when fetal brain development was assessed. Control animals received an isocaloric sucrose solution and were pair-fed to the experimental animals. An additional ad libitum control group was included. The alcohol treatment did not increase the incidence of the CC being absent in a midsagittal section. In BALB/c animals which had been exposed to ethanol the area of both the corpus callosum and anterior commissure was smaller than in the two control groups, and this effect was independent of the lower brain weight resulting from the treatment. The area of the corpus callosum, adjusted for brain weight, was smaller in both the alcohol-treated and sucrose control C57 animals than in the ad libitum control group; this suggests a nutritional effect. There was no evidence of an effect of ethanol on anterior commissure area or brain weight in C57 animals.