The mutagenicity of some pyrrole compounds were studied. Pyrrole compounds tested showed the mutagenicity on bacterial tester strains. Pyrrole and N-methylpyrrole had positive mutagenic activity on the ret-assay with Bacillus subtilis strains H 17 (Ret+) and M 45 (Ret-) in the absence of S-9 Mix. That pyrrole and N-methylpyrrole which had mutagenic action also exhibited DNA-breaking ability in the presence of Cu^<2+> was confirmed by agarose gel electrophoresis. But, the mutagenic action of pyrrole-22carboxylic acid by the ret-assay or DNA-breaking action was not confirmed.