TRAIL (TNF-Related Apoptosis Inducing Ligand) is a newly discovered cytokine able to induce apoptosis in tumor cells with a low toxicity to normal cells. TRAIL can induce apoptosis as a soluble trimeric molecule or as a ligand bound to the surface of effector cells. TRAIL induces apoptosis by binding to their receptors on the cell surface (TRAIL-R1 and TRAIL-R2). Three other receptors for TRAIL (TRAIL-R3, TRAIL-R4 and OPG) are receptors that anchor ligation not to induce apoptosis. Of the cell lines tested, 60% of the tumor cells are sensitive to TRAIL-induced apoptosis.