Because oxidative stress and inflammation are believed to play roles in the pathogenesis of cardiovascular diseases, oxidative stress in polymorphonuclear leukocytes (PMNs) and mononuclear cells (MNCs) has been measured. A total of 529 subjects participated this study. Intracellular oxidative stress in PMNs and MNCs was measured by gated flow cytometry using carboxyfluorescin diacetate bis-acetoxymethyl ester. C-reacting protein (CRP), insulin action (homeostasis model assessment), and traditional risk factors such as age, gender, body mass index, triglycerides, LDL cholesterol, HDL cholesterol, hemoglobin A1c, and mean blood pressure were also measured. Multiple regression analysis revealed a significant correlation between mean blood pressure and PMN oxidative stress (r=0.104,P=0.018). It also demonstrated a significant correlation between hemoglobin A1cand PMN oxidative stress (r=0.112,P=0.021). A significant correlation was also found between CRP and MNC oxidative stress (r=0.116,P=0.008) by multiple regression analysis. In patients with both hypertension and diabetes, both PMN and MNC oxidative stress was increased (n=21,P=0.022 andP=0.006). These results suggest that both hypertension and diabetes lead to increased oxidative stress of PMNs and MNCs, and that CRP is related to MNC oxidative stress.