Diallyl thioethers (DATEs), naturally occurring compounds present in garlic, were investigated for their putative ability to inhibit benzo[a]pyrene‐induced genotoxicity in ICR and C3H strains of mice. The mouse bone marrow micronudeus assay was used as an indicator of in vivo genotoxicity. A dose of 0.67 mmol total DATEs/kg body weight inhibited formation of micronucleated polychromatic erythrocytes (MPCEs) by 24%, and 0.33 mmol DATEs inhibited formation of MPCEs by 45%. Possibly the toxicity of DATEs accounted for less inhibition with the higher dose. Formation of MPCEs were inhibited only slightly by DATEs in C3H mice. These results indicate that the mouse bone marrow micronudeus assay can be used to identify organosulfur components of garlic that inhibit genotoxicity.