The Bcl-2 family of proteins is characterized by its ability to modulate cell death (apoptosis) under a broad range of physiological conditions. Bcl-2, A1 and Bcl-xL function to inhibit apoptosis while other members of the Bcl-2 family, Bax, Bad, Bak and Bcl-xS oppose their death-suppressing effects. Using a PCR-based strategy, an additional protein with life-promoting activity, designated Bcl-w, has been identified. The protein is highly conserved between mouse and human and is encoded by a gene located near the TCRα gene on chromosome 14. Bcl-w is expressed in myeloid cell lines but not in T and B lymphocytes, and can be found in a wide range of tissues. An alternative splicing event in exon 4 results in two transcripts. The first, Bcl-w, encodes a protein of 193 amino acids, and the second, Bcl-w/rox, encodes a protein 333 amino acids in length. The “rox” portion of Bcl-w/rox shows a striking 66% amino acid sequence identity with the Drosophila rox2 protein; however, the Bcl-w/rox transcript may be expressed at very low levels.