The antiviral function of pulmonary macrophages obtained by broncholavage of healthy smokers and nonsmokers was studied. Compared with nonsmokers' cells, smokers' macrophages produced significantly more virus during in vitro infection with herpes simplex virus type 1 (HSV-1). Exposure of macrophages to either antiviral macrophage-activating factor or interferon-gamma for 20 hr before infection resulted in diminished production of HSV-1 by both types of macrophages. However, in contrast to smokers' cells, exposure of nonsmokers' macrophages to these antiviral lymphokines totally prevented viral replication. This difference could not be attributed to diminished adsorption of virus to smokers' macrophages or to an increased proportion of extracellular to intracellular virus in smokers' cell cultures. The effect of smoking on viral infectivity did not appear to be mediated by secretion of a soluble factor by the macrophage because incubation of nonsmokers' cells with supernatant from smokers' cell cultures did not affect the growth of HSV-1.