The mechanisms underlying the teratogenic effects of alcohol are unknown, and may reflect metabolic differences between adult and fetal tissues. The liver is the major site of alcohol metabolism and the sole site of 25 hydroxyvitamin D synthesis. We have compared 25-hydroxyvitamin D production in adult nonpregnant, maternal, and pup livers obtained from vitamin D-deficient animals and examined the effects of alcohol ingestion on hepatic vitamin D metabolism. 25 Hydroxyvitamin D production was comparable in adult nonpregnant and maternal livers, but was decreased in pup livers compared to their maternal controls (1.4 ± 0.2 versus 0.6 ± 0.1 pmol/g protein/h,p< 0.001). Alcohol ingestion for 18 days had no effect on hepatic synthesis of 25 hydroxyvitamin D in the adult livers, but inhibited production by the pup livers (0.6 ± 0.1versus0.3 ± 0.1 pmol/g protein/h,p< 0.02). To assess the physiologic significance of these observations, the effect of alcohol on 25-hydroxyvitamin D levels in vitamin D-replete mothers and fetuses was determined. Alcohol had no effect on circulating 25 hydroxyvitamin D levels in the mothers but lowered fetal 25 hydroxyvitamin D content (2.3 ± 0.3versus1.2 ± 0.3 ng/g fetus,p< 0.02) without altering fetal weight. The data indicate that differences exist in pup and adult hepatic metabolism of vitamin D and that alcohol has inhibitory effects on pup liver function not expressed in adult tissues.