Preexposure of HL-60 cells to a DNA-damaging agent, cytosine arabinoside (Ara-C), dramatically induced the levels of H1 kinase activities associated with cyclin E (CycE-H1K) but not cyclin A. This induction was cell cycle-independent and accompanied by loss of cell viability, a late event in apoptosis. When an Ara-C-resistant variant of HL-60 cells were treated with Ara-C at a low concentration, neither CycE-H1K nor apoptosis were observed. Both events were induced in the resistant cells but only after treatment with Ara-C at a much higher concentration for a longer period. The DNA-damage-induced CycE-H1K is proposed to be involved in a late apoptosis checkpoint.