Abstract: To in estigate the levels of plasma antiox idant in patients with type Ⅱ diabetes mellitus,and to examine the relationship between plasma antiox idant levels and the development of complicaions in diabetes.A total of 33 pat ients with type Ⅱ diabetes mellitus(M/F 15/18,age 56.1±11.1 years)and 33 control subjects(M/F 16/17,age 56.0±10.5 years)w ere involved in the study.The levels of plasma antioxidants including vitamin A,vitamin E,enzyme superoxide dismutase(SOD)activity and the contents of nitric oxide(NO)were measured.Compared with age,sex-matched control subjects,no significant changes of plasma antiox idant vitamin A,E levels in patients with type diabetes mellitus were observed.The activity of SOD was reduced(P<0.05)and the content of NO was increased(P<0.01)in patients with diabetes as compared with controls.The results suggested tht an impaired antioxidant system might play a role in the pathogenesis of diabetes mellitus.