Abstract: To further study the relationship between resistance to apoptosis and drugresistance in harringtonine-resistant HL-60 cells(HR20),cyclosporine A(CsA)20,10 μg·ml^-1 wasshown to induce the sensitive HL-60 cells to apoptosis,showing a typical DNA“ladder”band.But thesame concentrations of CsA retarded the HR20 cells in G₁ phase and could not induce the cells toapoptosis.The cellular daunorubicin accumulation increased when HR20 cells were treated with lowconcentration of CsA and the reversal of drug resistance by CsA was unrelated to the retardation of cellcycle progression,High phosphorylation of about 50 kDa protein occured when HR20 cells weretreated with CsA 10μg·ml^-1. The results domonstrate that cyclosporine A retarded theharringtonine resistant HL-60 cells in G₁ phase but induced HL-60 cells to apoptosis,and theretardation was unrelated to drug resistance.