AbstractDay‐15 rat uteri were exteriorized under ether anesthesia and 100 μg 6‐AN + 500 μg oxidized (NAD;NADP) or reduced (NADH;NADPH) coenzyme; 500 μg adenosine triphosphate (ATP); or 100 μg nicotinamide (NAM) were injected into amniotic cavities in one horn. Embryos in the opposite horn served as injection controls. Mothers were closed and returned to their stock diet until autopsy on day 21 of gestation (day 0 = day of finding spermatozoa); fetuses were weighed, fixed, and examined for congenital abnormalities. Coenzymes, ATP, and NAM appeared to correct fetal and placental weight loss observed in 6‐AN‐treated fetuses. Vitamin and coenzyme therapy but not ATP treatment reduced the frequency and severity of brain and skeletal malformations to the double puncture, solvent control value. The data suggest that malformation and mortality may involve separate