Apoptosis, a selective process of genetically programmed cell death, occurs during normal cellular differentiation and development of multicellular organisms. Apoptotic cells are characterized by loss of cell volume, plasma membrane blebbing, nuclear condensation, chromatin aggregation, and endonucleocytic degradation of DNA into nucleosomal fragments. Caspase-3 (CPP32, Yama, apopain) is a member of the family of cysteine proteases which includes interleukin-1β converting enzyme (ICE) and C. elegans protein, Ced-3. An apoptotic signal such as granzyme B of cytotoxic T-cells (CTLs) or ICE-like proteases induces the intracellular cleavage of Caspase-3 from the inactive pro-form (32 kDa) to the active form which consists of the p20, p17, and p12 subunits. The active form of Caspase-3 cleaves several other apoptotic proteins including proteins such as DNA Fragmentation Factor (DFF). Apoptosis can be inhibited by coexpression of Bcl-2 as well as inhibitors of Caspase-3 or other members of the family of cysteine proteases. This antibody recognizes the human pro-form (inactive) of Caspase-3 at 32 kDa. In addition, it has been reported to recognize the active form of Caspase-3 at 20-21 kD in apoptotic cell lysates.