Induction of DNA fragmentation in apoptosis-sensitive HL-60 and Jurkat cells but not in apoptosis-resistant Raji cells. The cells were treated with 50 μmol/L t-BHP for 4 hours at 37°C and were then harvested for DNA isolation. Characteristic apoptotic DNA ladders were observed in HL-60 and Jurkat cells but not in Raji cells. This experiment was repeated more than 3 times with similar results.