Aim To investigate effects of L-arginine and N~G-nitro-L-arginine methyl ester(L-NAME) on human umbilical vein endothelial cell(hUVEC) secreting nitric oxide(NO) and superoxide anion(O_2~-). Methods hUVEC was incubated with glucose,insulin,L-arginine and L-NAME respectively for 24 hours.The activity of nitric oxide synthase(NOS) and superoxide dismutase(SOD),the concentration of NO and O_2~-in the supernatant of cultured hUVEC was measured at the end of the experiment. Results NOS activity,the concentration of NO increased,while SOD activity decreased and the concentration of O_2~-increased significantly in the presence of 25 mmol/L glucose.NOS,NO,SOD did not change significantly in the presence of L-arginine,while the concentration of O_2~-decreased significantly. The activity of NOS,the concentration of NO increased in the presence of 25 mmol/L glucose+L-arginine,L-arginine may reverse the elevation of O_2~-which induced by glucose.NOS,NO increased in the presence of 10,100,1 000 mu/L insulin,while SOD and O_2~-did not change significantly.NOS,NO increased in the presence of L-arginine+insulin,SOD activity did not change significantly while O_2~-decreased.NOS activity and the generation of NO decreased in the presence of 100 μmol/L L-NAME,while SOD activity did not change significantly,however the generation of O_2~-increased.NOS,NO decreased in the presence of 25 mmol/L glucose+L-NAME,however SOD activity and the concentration of O_2~-did not change significantly.NOS,NO decreased in the presence of 10 mu insulin+10 μmol/L LNAME and 100 mu insulin+100 μmol/L L-NAME,SOD activity did not change significantly,while the concentration of O_2~-increased. Conclusion NOS,NO,SOD did not change significantly while O_2~-decreased in the presence of L-arginine.NOS activity,the generation of NO decreased while O_2~-increased in the presence of L-NAME in the supernatant of cultured endothelial cell.