Objective The present study was designed to investigate changes in serum or plasma concentrations of nitric oxide and its derivatives in diabetic patients. Methods Serum nitrate concentration of 84 diabetic patients was measured by using an enzyme kinetic method, and the plasma S-nitrosothiols concentration of 10 cases was measured by using HPLC technique. Results Serum nitrate concentration and plasma S-nitrosothiols concentration in the diabetics were significantly higher than in control group (P<0.01 and P<0.05, respectively). The serum nitrate concentration in diabetics also had a significant positive correlation with the serum glucose concentration (R=0.7256, P<0.05), but this correlation was not found in control group. Conclusion These data showed that NO and its derivatives are overproduced in the diabetic patients.