The effects of ethanol on the physical development and maturation of the CNS in the offspring of lactating rats were investigated. Dams were fed: 1) regular stock diet (control), 2) liquid diet containing 35% of the calories as ethanol (ETOH) or 3) liquid diet with maltose-dextrin substituted for the calories supplied by ethanol (isoenergetic = IE). Diets were administered from the 14th day of gestation until 3 weeks post-partum (pre- and post-natal exposure) or from birth until 3 weeks post-partum (post-natal exposure). Body weight, crown-rump length and tail length, as well as brain weight were followed longitudinally in the pups. The growth in the pups of dams fed ETOH diet and those fed IE diet were significantly less than that observed in the pups of control dams. Furthermore, pups of dams fed the ETOH diet showed retardation in growth indices and brain weight at various ages when compared to pups of equivalent age from dams fed the IE diet. Therefore, administration of ethanol to pregnant or lactating dams impaired the physical growth, including central nervous systems (CNS), of their offspring more than those changes caused by nitritional deprivation.