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Background: Human serum paraoxonase is physically associated with HDL and has been implicated in the detoxification of organophosphate and possibly in the prevention of LDL lipid peroxidation. The activities of paraoxonase and levels of HDL cholesterol were measured in the serum of individuals with type 2 diabetes mellitus in order to evaluate whether a correlation exists between these cnzyme activities and the diabetes mellitus and dliabetic complications. Methods: Plasma samples were obtain from 60 individuals with type 2 diabetes mellitus(32 women and 28 men; mean age=55.8 yrs) and 30 individuals with healthy control(16 women and 14 men; mean age=-54.1 yrs). Paraoxonase activities were measured spectrophotometrically in 0.1IM Tris-HC1 buffer(pH= 7.4) at 25C with paraoxon as substrate(5.5mM) at 405nm. Results: No significant differences of plasma paraoxonase activity between healthy control and type 2 diabetes mellitus were observed. The signifi- cant difference of plasma paraoxonase activity between healthy control and type 2 diabetes mellitus with diabetic complications such as diabetic neuropathy, diabetic retinopathy and diabetic nephropathy were observed. The difference of plasma paraoxonase activity between individuals with type 2 diabetes mellitus without diabetic complication and type 2 diabetes mellitus with diabetic complications was significant. The correlation between paraoxonase activity and HDL-cholesterol, plasma lipoproteins, HbAlc and duration of diabetes were not observed. Conclusion: These experimental results suggested that the plasma paraoxonase activity wasnt decreased in individuals with type 2 diabetes mellitus without diabetic complication and the decrement of plasma paraoxonase activity was might be associated with diabetic chronic complications.