Prenatal ethanol exposure produces neural tube defects and growth retardation in experimental animals. Because ethanol's teratogenic effects may involve oxidative stress and effects may differ in vitro and in utero, glutathione, cysteine and ATP were evaluated in gestational day 10 rat conceptuses exposed to ethanol. Cultured embryos exposed to ethanol (1.5 or 3.0 mg/mL) maintained a concentration-dependent decrease in glutathione of 21 or 35%, respectively, at 6 h; visceral yolk sac (VYS) glutathione (GSH) decreased by 22 or 18%, respectively, at 3 h. Maternal ethanol exposure (4.5 g/kg) decreased glutathione by 30% in embryos and VYSs at 3 h, but values rebounded. Cultured embryonic cysteine decreased after 30 min by 42% with both doses and after 6 h by 32 or 38% with 1.5 or 3.0 mg/mL, respectively. Ethanol (1.5 mg/mL) increased VYS cysteine by 35% after 30 min. In utero ethanol exposure decreased embryonic cysteine by 58% at 3 h. Ethanol (1.5 mg/mL) decreased adenosine triphosphate (ATP) by 30-60% in embryos and VYSs at 30 min. After 6 h, embryonic ATP decreased by 41 and 30% with 1.5 and 3.0 mg/mL, respectively, while VYS ATP decreased by 38% with 1.5 mg/mL. In utero ethanol exposure decreased ATP by 31% at 3 h in VYSs. While decreases in GSH and cysteine were evident earlier in utero than in vitro, values returned to control suggesting embryos exposed in utero respond rapidly to chemical-induced oxidative stress due to maternal protective mechanisms. Differences between in vitro and in utero responses to ethanol have important implications for interpretation of in vitro developmental studies.