The mutagenicity of refuse leachate from a municipal incinerator was studied by liquid rec-assay and Ames assay. Volatile components were found to be negative, and nonvolatile components positive, in the Ames assay and the leachate was found to have DNA-damaging capacity in the liquid rec-assay with S-9 mix. PAHs derived from tobacco ash and carbonyl compounds generated by the putrefaction of foods were confirmed to be main contributors to DNA-damaging capacity and mutagenicity in refuse leachate.