In order to investigate the occurrence of hyperleukocytosis in treating acute promyelocytic leukemia (APL) patients with all trans retinoic acid (ATRA) and to explore the influence of the level of leucocyte on curative effect of ATRA, the APL patients were divided into three different groups according to the count of leucocyte in peripheral blood. Patients with WBC count less than 30x10(9)/L were administered with ATRA alone (the first group), patients with WBC count more than 30x10(9)/L were administered with ATRA alone (the second group) and patients with WBC count more than 30x10(9)/L were treated with ATRA+cytotoxic drugs (the third group). The results showed that hyperleukocytosis were found in 23 out of 39 patients (58.97%). Total remission rates in the second group and in the third group were 91.3%. The remission rates in the first, second and third groups were 100%, 87.5% and 90.9%, respectively. It is concluded that the ATRA in combination with cytotoxic drugs can efficiently control the occurrence of hyperleukocytosis during ATRA-treating APL and reduce the early mortality.