We have infected peripheral blood-derived monocyte/macrophage cultures with HIV-1 in order to determine the effect of such infection on cellular immunoregulatory function. We have confirmed that monocytes/macrophages are susceptible to infection by HIV-1, as determined by in situ hybridization using a HIV-1-specific RNA probe and by the presence of reverse transcriptase activity in culture supernatants. The cells employed efficiently supported viral replication in the absence of significant cytopathic effect, and secreted as little as 20% of the amount of IL-1 activity of uninfected controls in response to stimulation with either latex beads or lipopolysaccharide. This effect was not observed when UV-inactivated HIV-1 was used to infect the cells.