Drosophila provides a powerful genetic model for studying the in vivo regulation of biological processes, such as cell proliferation, cell differentiation, and cell death. In a large-scale ectopic-expression screen in Drosophila for identifying genes regulating cell death, the fly homolog of tumor necrosis factor (TNF) encoded by eiger (e da-l i ke cell death trig ger) was identified . eiger was also isolated independently through a molecular approach . eiger encodes a protein of 409 amino acids with a C-terminal TNF homology domain and a hydrophobic transmembrane domain. The sequence of the Eiger's TNF domain shows highest homology with human EDA-A2 (28%) and also shows significant homology with all known mammalian TNF superfamily members.