The capacity of the cytokines gamma interferon (IFN-gamma), interleukin-4 (IL-4), and tumor necrosis factor (TNF) to activate tuberculostatic functions in murine bone marrow-derived macrophages (BMM phi) was investigated. In confirmation of earlier findings, IFN-gamma rendered BMM phi capable of inhibiting subsequent infection with Mycobacterium bovis. In contrast, IL-4 and TNF failed to inhibit mycobacterial growth. However, in already infected BMM phi, tuberculostasis was induced by subsequent stimulation with IL-4. Although TNF alone was ineffective, it showed synergy with IFN-gamma in the stimulation of tuberculostasis. Our data suggest that not only IFN-gamma but also IL-4 and TNF participate in the control of mycobacterial growth.