Objective To identlfy the member of the caspase famlly proteases involved in Y-radiation-inducedapoptosis in HL-60 cells and to study the expression or the caspase gene in normal, apoptotic cells and in immortal tumor cells. Methods By using degenerate oligonucleotide primers encoding the highly conserved peptides that were present in all known caspases, we performed RT-PCR on poly(A)RNA from γ-radiation-induced apoptotic HL-6o cells.Caspase-3 mRNA in apoptotic HL-6o cells and in human tumor cell lines was analyzed by Northern blot. Results The amplified DNA fragment was identiried with caspase-3 cDNA by cloning and sequencing. The Northern blot analysis of caspase-3 mRNA of different human tumor cell lines showed that the caspase-3 gene transcript was more highly expressed in leukemia cell lines and the SH-SY5Y cell line than in HeLa and MCF-7 cells. It was more highly expressed in the radiation-induced apoptotic HL-6o cells than in control HL-6o cells. Conclusion These results indicated that caspase-3 was involved in γ-radiation-induced apoptosis in HL-6o cells. The high level of expression or caspase-3 may aid efforts to understand the insensitivity of some tumor cells to radlation, their inherent ability to survive, and apoptosis Objective To identlfy the member of the caspase famlly proteases involved in Y-radiation-inducedapoptosis in HL-60 cells and to study the expression or the caspase gene in normal, apoptotic cells and in immortal tumor cells. Methods By using degenerate oligonucleotide primers encoding the highly conserved peptides that were present in all known caspases, we performed RT-PCR on poly (A) RNA from γ-radiation-induced apoptotic HL-6o cells. Caspase-3 mRNA in apoptotic HL-6o cells and in human tumor cell lines was analyzed by Northern blot. Results The amplified DNA fragment was identiried with caspase-3 cDNA by cloning and sequencing. The Northern blot analysis of caspase-3 mRNA of different human tumor cell lines showed that the caspase-3 gene transcript was more highly expressed in leukemia cell lines and the SH-SY5Y cell line than in HeLa and MCF-7 cells. It was more highly expressed in the radiation-induced apoptotic HL-6o cells than in control HL-6o cells. ated that caspase-3 was involved in γ-radiation-induced apoptosis in HL-6o cells. The high level of expression or caspase-3 may aid efforts to understand the insensitivity of some tumor cells to radlation, their inherent ability to survive, and apoptosis