The umu-test, which can detect genotoxic activites of a wide variety of environmental carcinogens and mutagenes, was carried out with samples from several sewage treatment processes. We applied the umu-test to raw sewage and treated effluent from two points of view, one is to evaluate a treatment process and the other is to identify the genotoxic substances. The original strain of umu-test, Salmonella typhimurium TA1535/pSK1002 can detect nonspecific genotoxicity, on the other hand, by using S. typhimurium NM2009 of the umu-test highly sensitive to aromatic amines, genotoxicity related to aromatic amines is measured. The result showed that genotoxic substances which have the polycyclic aromatic amino structures in the sewage remained after biological treatment. Tow-step HPLC fractionation followed by MS analysis to identify the genotoxic substances was applied to samples to detect mutagenic and carcinogenic heterocyclic amines. The concentration of Trp-P-1 and Trp-P-2 determined in the effluent caluculated from HPLC-UV analysis were on the order of 10(-5) mg/L. Because of the possibility of the reuse of wastewater in urban areas, the need for the investigation of the safety of the treated water from the sewage treatment plants was suggested, in order to evaluate strategies for advanced treatment, if necessary.