This study investigated the level of platelet malondialdehyde (MDA) as a marker of oxidative stress and coenzyme Q10 (CoQ10) as an index of antioxidant capacity in patients with type 2 diabetes mellitus and their relation to glycemic control. The study group consisted of 28 patients with type 2 diabetes mellitus (10 men and 18 women) with mean age of 48 +/- 2 years. Ten healthy individuals, age and sex matched with the patients, were used as a control group. Laboratory investigations in the form of lipid profile, glycosylated hemoglobin, plasma MDA, platelet MDA and plasma CoQ10 were assessed for all patients and controls. The study revealed that plasma and platelet MDA, as a marker of oxidative stress, were significantly higher in diabetic patients than in controls. The level of CoQ10, as antioxidant capacity, was significantly lower in diabetic patients than in controls. There was a negative correlation between plasma CoQ10 concentrations and glycosylated hemoglobin. Type 2 diabetic patients are at increased risk of oxidative stress manifested by increased plasma MDA as well as platelet MDA and decreased CoQ10, and this oxidative stress increases with poor glycemic control.