Thirty-two pregnant Long-Evans rats were divided into 10 groups of 3 or 4 pregnant rats, and each rat was given a single dose of 4 ml ethanol/kg (20 ml/kg of a 20% solution) between d 6 and 15 of gestation. An 11th group of 50 pregnant rats received distilled water and served as controls. Offspring body weights were decreased in groups of rats given ethanol as compared to controls (3.0-3.6 g, versus 3.9 g for controls). Total litter weight was decreased in dams given ethanol on d 6. Skeletal variants were seen in 13-78% of the offspring given ethanol, compared to 0.6% of the controls. Variations may be considered as additional signs of embryotoxicity. Malformations such as hydronephrosis, pelvic kidney, microcephalus, cranioschisis, and microphthalmia occurred in 72-100% of the ethanol treated offspring, as compared to 12% of controls. Hydronephrosis was most frequent on d 9 or 14, pelvic kidney on d 8 and 11, and microphthalmia from d 10-12. Cranioschisis was maximal on d 7, 11, and 15, and microcephalic offspring were most frequently born to dams given ethanol on d 7 or 14. Skeletal defects were usually single entities, while soft-tissue anomalies occurred in a consistent pattern. These results suggest that ethanol is a stage-specific teratogen in the rat at comparable exposure levels attained by many humans.