Human monocyte derived macrophages (MDM) cultured in medium containing macrophage (M) CSF are more susceptible to infection with HIV-1. M-CSF increases the frequency with which MDM become infected, the level of HIV mRNA expressed per infected cell, and the level of proviral DNA expressed per infected culture. Because of these effects of M-CSF on HIV-1 replication and the reported function of this factor as a survival and differentiation factor for human monocytes, we investigated whether HIV-1 could induce endogenous M- CSF production by MDM and the potential role of endogenous M-CSF on HIV-1 infection in these cells. MDM infected with HIV and maintained in the absence of exogenous M-CSF produced this cytokine endogenously at levels 5 to 24- fold higher than uninfected cells. In contrast, the proinflammatory cytokines IL-1, IL-6, and TNF-α and the growth factor granulocyte-macrophage CSF were not detected. The kinetics of M-CSF production following infection paralleled the kinetics of virus replication. Furthermore, enhanced production of M-CSF was dependent on vital entry and active replication of HIV-1. Thus, endogenous M-CSF production may contribute to the survival of HIV-infected MDM, enable them to function as a reservoir for HIV, and facilitate the spread of virus in vivo.