This cell line was derived from peripheral blood leukocytes obtained by leukopheresis of a 36-year-old Caucasian female with acute promyelocytic leukemia. HL-60 cells spontaneously differentiate. Differentiation can be stimulated by butyrate, hypoxanthine, phorbol myristic acid (PMA, TPA), dimethylsulfoxide (DMSO, 1% to 1.5%), actinomycin D, and retinoic acid. The cells exhibit phagocytic activity and responsiveness to chemotactic stimuli.