Members in the Bcl-2 family are critical regulators of apoptosis by either inhibiting or promoting cell death. Bcl-B is a recently discovered anti-apoptotic member of the Bcl-2. Unlike the mouse homolog (also known as Diva/Boo) which is predominantly expressed in ovary and testis, the human Bcl-B protein is widely expressed. Also, the human Bcl-B functions by binding to and suppressing the apoptotic activity of Bax, whereas the mouse homolog binds Bak and also interacts with the apoptosis protein Apaf-1. Despite its predicted molecular weight, Bcl-B is often at higher molecular weights, presumably due to post-translational modifications.