Salmonella typhimurium strains TA100, TA104, TA4001, and TA4006 were used to detect the base-pair mutations caused by six aliphatic epoxides: chloropropylene oxide, glycidyl 1-naphthyl ether, glycidyl 4-nitrophenyl ether, 1-naphthyl-propylene oxide, styrene oxide, and trichloropropylene oxide. Dose-mutagenicity relationships could be established for all six epoxides in strains TA100 and TA104 but not in strains TA4001 and TA4006. These results, together with the lack of sensitivity of the TA100 revertants to DL-1,2,4-triazole-3-alanine, indicate CG-->TA transitions and/or CG-->AT transversions are of major importance for mutations induced by these epoxides in Salmonella TA100 and possibly TA104. In addition, since the reproducibility of the effect of the triazole on TA104 reversions was poor, TA-->AT transversions were not eliminated as also contributing to the mutagenicity of these epoxides in this Salmonella strain.