Abstract: This invention relates to antibodies or fragments thereof that can be used as indicators of apoptosis. More specifically, this invention relates to antibodies and fragments thereof that selectively bind GP46, a protein whose levels increase significantly upon induction of apoptosis. This invention also relates to the hybridomas that produce anti-GP46 monoclonal antibodies. This invention also discloses a method of detecting cell death by apoptosis in vitro or in vivo by detecting and quantifying GP46 present in biological samples, comprising contacting the sample with the antibodies or fragments to form GP46 immunocomplexes, which may then be detected by the use of known methods. This detection method is useful for research into apoptosis and research relating to diseases in which apoptosis is involved. This method could also be used to diagnose the extent of damage caused by a particular disease or to evaluate the efficacy of drug treatments.