A protein corresponding in size to the bcl-2 alpha protein obtained after in vitro transcription and in vitro translation in a rabbit reticulocyte lysate was specifically immunoprecipitated from a human B-cell extract using rabbit polyclonal antiserum raised against a beta-galactosidase/bcl-2 fusion protein. Peptide mapping with V8 protease confirmed the identity of this protein as human bcl-2 alpha. Subcellular fractionation of cellular protein followed by immunoprecipitation showed that the bcl-2 alpha protein is associated with the cell membrane.