Abstract: "The mutagenicities of the various organic fractions of the exhaust particulates from the diesel (trademark : Yuejin) were studied by micronucleus test on bone marrow polychromatid erythrocytes (PCE,in vivo) in mice and Chinese hamster ovarian cells (CHO in vitro). The results showed that all the five fractions of the diesel exhaust particulates could significantly increase the frequencies of micronucleus of PCE and CHO，in comparison with DMSO control (P＜0.05 or P＜0.01),and the dose - response relationships were apparent. The mutagenicities of organic bases，polycyclic aromatic hydrocarbons and polar compounds were higher than those of the other fractions. "