High-dose cytarabine chemotherapy regimens were given to 22 patients for the treatment of blastic phase chronic myelogenous leukemia. Bone marrow aplasia occurred in 21 of these patients; in one patient the marrow was not cleared of blasts. In five patients (26%), blastic phase promptly recurred. Eight patients (37%) died of infection or hemorrhage during the period of marrow aplasia before bone marrow recovery. Seven patients achieved complete remission and one achieved partial remission, but the duration of the remission was brief [median, 98 days (range, 52-345)]. One patient received consolidation therapy with an additional course of high-dose cytarabine and maintained remission for 345 days. These results suggest that alternative approaches to the treatment need to be explored.