It is important to have a rapid and accurate method to detect the toxic action of drugs and chemical compounds used by man. A comparative study with two microbial systems was carried out: one using Salmonella typhimurium and the other using Bacillus subtilis. The 1-8-dihydroxyantraquinone was the tested drug and the N-methyl-N'-nitro-N-nitrosoguanidine and the 2-aminofluorene were used as control substances. These compounds were used as such or after previous transformation by a microsomal system. The results obtained showed that both systems: the S. typhimurium and the B. subtilis work in a similar way, but the latter allows a more direct action of drug on the genetic material. The effect of the solvents: ethanol and dimethylsulfoxide was analysed, because they affected the transformation and reversion processes that were carried out.