The clastogenic effects of the diesel emission particle extract (DEPE), mercuric chloride and lead acetate were examined by the mouse bone marrow micronucleus test. DEPE had a potent clastogenic effect by intraperitoneal injection with dose-response between 100 and 300mg/kg b.w.. Mercuric chloride and lead acetate also gave a clastogenic effects but mercuric chloride only had a dose-response between 1 and 3mg/kg b.w.. When DEPE was administrated with mercuric chloride or lead acetate, the frequency of micronucleated cells was slight but not significant increase in comparision to a single treatment with DEPE alone.