Abstract: Effects of five antitumor drugs on the murine normal hemopoietic and P₃₈₈ leukemic colony-forming cells were studied and compared by means of spleen colony assay. Dose-survival curves for the normal spleen colony-forming units (NCFU-S) and the leukemic spleen colony-forming units (LCFU-S) exposed to harringtonine (H), partial synthetic harringtonine (PSH), homoharringtonine (HH), and cyclophosphamide (CP)exhibited exponential forms. The value of efficacy ratios of the four drugs was 5.15, 6.01, 7.96, and 9.98 in the following order for H, PSH, HH, and CP, respectively. All dosage levels of arabinosylcytosine (Ara-C)used showed no distinct effect on the NCFU-S, but exhibited a strong effect on the LCFU-S with increasing dosage; the dose-survival curve for LCFU-S was decreased to a plateau value of 0.2% at the dosage of 500-1000 mg/kg. No obvious effect of H, HH, and PSH on the dose-survival curves was observed when the doses used were less than 0.3, 0.28 and 0.75 mg/kg, respectively.