Human immunodeficiency virus type 1 (HIV-1) infects mononuclear phagocytes, cells that may serve as a reservoir for viral persistence. Infection with HIV-1 leads to progressive compromise of the immune system, resulting in infections with opportunistic pathogens and eventual death. Experiments were designed to determine if in vitro HIV-1 infection of mononuclear phagocytes would diminish their oxidative capabilities, thus decreasing their antimicrobial effectiveness. Blood monocytes and peritoneal macrophages were obtained from uninfected donors and inoculated with a monocytotropic strain of HIV-1. Hydrogen peroxide production and reduction of nitroblue tetrazolium were measured after acute stimulation of cells with PMA or a phagocytic stimulus. Despite vigorous virus production, no difference was seen in oxidative burst between uninfected cells and infected cells or between monocyte-derived and peritoneal macrophages. In conclusion, reduced antimicrobial activity of HIV-infected mononuclear phagocytes is probably not secondary to decreased ability to generate reactive oxygen species.