The invention provides Bcl-G polypeptides and encoding nucleic acids. Bcl-G polypeptides include Bcl-G.sub.L and Bcl-G.sub.S. The invention also provides mouse Bcl-G. The invention also provides vectors containing Bcl-G nucleic acids, host cells containing such vectors, Bcl-G anti-sense nucleic acids and related compositions. The invention additionally provides Bcl-G oligonucleotides that can be used to hybridize to or amplify a Bcl-G nucleic acid. Anti-Bcl-G specific antibodies are also provided. Further provided are kits containing Bcl-G nucleic acids or Bcl-G specific antibodies. Such kits and reagents can be used to diagnose cancer, monitor response to therapy, or predict the prognosis of a cancer patient. The invention additionally provides methods of modulating apoptosis using Bcl-G polypeptides, encoding nucleic acids, or compounds that modulate the activity or expression of Bcl-G polypeptides. The methods for modulating apoptosis can be used to treat diseases such as cancer.