Abstract Pregnant mice of the CBA/J and C57BL/6J strains were given either tertiary butanol (10.5 mmoles/kg, p.o.) or an equivalent volume of tap water twice daily from day 6 through day 18 of gestation. Examination on day 18 revealed significantly more resorptions per litter in the t-butanol-treated animals but no interstrain difference. Tertiary butanol did not significantly affect the body weight of the survivors nor produce significant abnormalities in either strain. Subsequent blood concentration profiles in female C57BL/6J mice indicated that the treatment regimen produced blood levels equivalent to teratogenic ethanol treatment. Mice receiving 3 days of t-butanol treatment did not eliminate the drug more rapidly than control animals, indicating that tolerance was not a factor in the treatment regimen. Since t-butanol shares membrane disordering effects with ethanol but is not metabolized by the same pathway, a role for acetaldehyde or the process of ethanol metabolism is suggested in ethanol teratogenicity.