Tumor necrosis factor related apoptosis-inducing ligand (TRAIL), which called also Apo-2L, is a new member of the tumor necrosis factor superfamily. TRAIL cDNA was isolated via searching homology to Fas/Apo-1 ligand and TNF in an expressed sequenced tag (EST) data base. It consists of 281 amino acids with a calculated molecular mass of 32.5 ku. Transfected TRAIL is expressed at the cell surface with its C-terminus exposed, indicating a type Ⅱ transmembrane protein topology. Like Fas/Apo-1 ligand and TNF, its C-terminal exhibits a homotrimeric subunit structure. Soluble TRAIL induces extensive apoptosis in most tumor cell lines, but the effect of TRAIL is not inhibited by soluble Fas/Apo-1 and TNF receptors. So far, three receptors of TRAIL have been identified, i.e. DR4, DR5 and TRID. These discoveries suggest that the mechanism of TRAIL is different from TNF and FasL. TRAIL may likely be elaborated as a new anti-cancer drug.