Tumors of diverse origin have recently been shown to express CD95 ligand and to induce apoptosis in CD95-expressing targets in vitro; however, in vivo, enhanced tumor growth and rejection have both been observed as a consequence of either immunosuppressive or proinflammatory functions of CD95 ligand. The final in vivo outcome of CD95 ligand expression will depend upon a complex balance of interactions relevant for each tumor in its particular microenvironment.