The role of nitric oxide (NO) in HIV infection is ambiguous; controversy exists around whether the levels of serum NO are increased or decreased in HIV-infected patients. Thus, it is necessary to reassess NO levels in HIV-infected patients. The aim of this study was to investigate the nitrite/nitrate metabolite (NOx) levels in HIV-infected untreated patients and in HIV-infected patients receiving highly active antiretroviral therapy (HAART), compared with HIV-uninfected individuals (control group). The HIV-infected patients enrolled in this study had been receiving HAART for at least 6 months (HIV-treated) or had not received HAART for at least 6 months (HIV-untreated group). New recommendations encourage initiating treatment in HIV-infected adults at a CD4 cell count of 500 cells/mm³ or less. We also investigated whether levels of NOx were associated with immunophenotypic characteristic of HIV-infected patients. Our results showed a statistically significant increase in NOx levels in the HIV-untreated group (164.0±166.6μmol/L), compared with both the control (98.9±59.4μmol/L) and HIV-treated group (71.7±53.3μmol/L). Multiple regression analysis showed that the differences in NOx level were independent of gender, liver enzyme level, lipid measurement, and hematological parameters. In addition, a lower CD4/CD8 ratio was associated with higher NOx levels in HIV-infected patients. The results further revealed that NOx levels were increased in HIV infection, and that derangement of immune system function was associated with increased NO levels. The levels of NOx were found to decline with the use of HAART, which may contribute to cardiovascular disease in HIV-infected patients.