Adult female mice, male rats, female hamsters and male guinea pigs received various doses of styrene (150-1000 mg/kg of body wt) and acrylonitrile (20-80 mg/kg of body wt) i.p. Both styrene and acrylonitrile caused a depression of the hepatic nonprotein sulfhydryl content. Mouse was the most vulnerable and rat the most resistant species to the effect of both of these 2 important plastic monomers. [Since many people are exposed to styrene and acrylonitrile, the health implications of these 2 monomers, widely used in industry, are of considerable interest.].