The purpose of this study was to determine the extent of oxidative stress in NIDDM patients with diabetic complications and to determine the relationship between oxidative stress and diabetic complications. For this study, 139 NIDDM patients were recruited, 85 with diabetic complications and 54 without complications were recruited. The concentration of malondialdehyde(MDA) and the activities of antioxidant enzymes including catalase, superoxide dismutase(SOD), gluthatione peroxidase(GSH-Px)were determined. The daily intakes and plasma concentrations of beta-carotene, lycopene, lutein nd alpha-tocopherol were determined by food frequency questionnaire and by high performance liquid chromatography(HPLC), respectively. Among the antioxidant enzymes studied, only GSH-Px activity was lower in NIDDM patient, with diabetic complications than in those without complications(2.91$pm$0.80 vs 3.54$pm$0.44 U/mgHb, p<0.05). Those NIDDM patients with diabetic complications had higher MDA concentrations than those without diabetic complications(1.40$pm$0.25 vs 1.25$pm$0.11 nmol/ml, p<0.05). There were no significant differences in the dietary intakes of total carotenoids(2854 vs 2824ug/day)or vitamin E (9.5$pm$3.2 vs 9.5$pm$2.0mg/day)between NIDDA patients with and without complications. However, the plasma concentrations of beta-carotene and lycopene were significantly lower in NIDDM patients with complications than in NIDDM patients without complications (Beta-carotene : 24.2$pm$12.5 vs 33.1$pm$16.2(ug/dl), lycopene : 2.8$pm$2.1 vs 4.3$pm$2.8(ug/dl)). This study showed that in NIDDM patients with complications, the lipid peroxidation of erythrocytes was higher increased and the antioxidant reserves were significantly dipleted, compared with NIDDM patients without complications. The lower plasma concentrations of beta-carotene and lycopene in NIDDM patients may be due to the presence of diabetic complication, not due to the lower dietary intakes of antioxidant vitamins. To define the role of carotenoids in diabetes, more experimental and clinical studies are needed.