Neutrophils from asymptomatic HIV-infected patients have an increased Nitroblue tetrazolium (NBT) reduction, that is an increased production of oxygen radicals. Plasma from these patients can activate normal neutrophils to an increased NBT-reduction and the neutrophil activating factor thus seems to be mainly plasma bound. Further, the patients also have increased levels of plasma malondialdehyde and thus an increased lipid peroxidation. Plasma cysteine levels are low, a sign of increased consumption of antioxidants. Treatment of the asymptomatic HIV-infected patients with N-acetylcysteine corrected the plasma cysteine levels and had some beneficial effects, but did not inhibit the increased radical production by the neutrophils.