Abstract: The cell cycle flow cytometric analysis of marrow in patients with acute leukemia during diagnosis, first relapse and remission was done and compared with the that when marrow was normal. The mean percentage of S/G₂M phase cells （S/G₂M%） was signifcantly higher dvring relapse and remission than at diagnosis, （P＜0.001） indicating a changed proliferative activity. In most patients in remission, the S/G₂M cells were close to the normal, reflecting diferent degrees in recovery of normal hemopoiesis. The S/G₂M% was normal in 3 patients sustaining complete remission after allogeneic bone marrow transplantation, which was considered as the result of reconsti-tution of donor hemopoiesis.