Bcl-2 is a 26 kDa member of the family of proteins involved in regulation of programmed cell death, or apoptosis. It is expressed in a variety of both normal and neoplastic tissues and appears to be membrane-bound since it is detectable in crude membrane and nuclear fractions, but not in the soluble fraction of cell lysates. Overexpression of Bcl-2 can prevent apoptosis, while formation of heterodimers with Bax, another Bcl-2-related protein, inhibits Bcl-2’s ability to promote cell survival.