Abstract: In order to explore the role of nitric oxide(NO)and nitric oxide synthase(NOS)in dust(quartz and asbestos)-caused diseases,rabbit avleolar macrophages collected by Myvirk method were cultured in vitro.NO₂^-/NO₃^-,the stable oxide formation of NO,in the culturing supernatants of TiO₂-,quartz-and chrysotile-treated AMs was measured by nitrate reductase reaction method,and NOS activity was measured with color reaction method(enzyme-substant reaction).The results showed that with the increase of dust concentration,(1)AM mortality increased in both quartz and chrysotile group,the effect of different dust was different:chrysotile>quartz>TiO₂.(2)In both quartz and chrysotile groups,NO₂^-/NO₃^- increaed with dose-response relationship(P<0.05);at the higher dose group,NO in both groups was higher than that of TiO₂ group respectively,but there was no difference in quartz and chrysotile group(P>0.05).(3)NOS activity elevated in quartz and chrysotile groups,but in 100,200μg/ml chrysotile group,the NOS activity decreased,which was maybe result from AM mortality increasing.(4)The change of NO was agreement with the change of NOS activity in quartz-and chrysotile-exposed AMs.It was suggested that NO and NOS were maybe potential role in quartz-and chrysotile-related diseases.