CD8+ cell clones have been derived from peripheral blood mononuclear cells of human immunodeficiency virus (HIV)-infected and uninfected individuals. Several of these cloned cells have the ability to suppress HIV replication when cocultured with CD4+ cells acutely infected in the laboratory with HIV or with infected CD4+ cells from infected subjects. Suppression of virus production occurs without killing the target cells. With the CD8+ cell clones studied, this antiviral response correlated with production of a filterable factor that has antiviral activity. These cell clones offer the opportunity for identification of the factor mediating suppression of HIV replication. Moreover, adoptive transfer of cell clones might provide a valuable therapeutic approach for HIV-infected individuals.