Objective:To investigate the cell-cycle specificities of cytarabine and paclitaxel in different growing status of target cell.Methods:Using flow cytometry,we tested the cell-cycle specificities of cytarabine and paclitaxel on acute lymphocyte leukemia cell line Molt-4 in different growing status and on clinical acute lymphocyte leukemia specimens in vitro as well as in leu-kemia patients in vivo.Results:Cytarabine induced S phase specific cell-cycle blockage and apoptosis in exponentially growing Molt-4,but showed G0/G1 phase specificity in high-density cultured Molt-4 and in clinical specimens.Paclitaxel induced G2/M phase specific cell-cycle blockage and apoptosis in exponential Molt-4,but showed G0/G1 phase specificity in high-density cultured Molt-4 and S phase specificity in clinical specimens.In the first day of clinical chemotherapy,cytarabine induced G0/G1 with a little S phase apoptosis in leukemia cells of acute lymphocyte leukemia patient in vivo.Cytarabine plus paclitaxel together had almost the same effect in the second day.Conclusion:The cell-cycle effects of cytarabine and paclitaxel were different in different target cell growing status.It should be noted that the in vivo effect of these agents may be different from people usually anticipated during clinical chemotherapy.So the combined chemotherapeutic regimens may need to be redesigned. Objective: To investigate the cell-cycle specificities of cytarabine and paclitaxel in different growing status of target cells. Methods: Using flow cytometry, we tested the cell-cycle specificities of cytarabine and paclitaxel on acute lymphocyte leukemia cell line Molt-4 in different growing. status and on clinical acute lymphocyte leukemia specimens in vitro as well as in leu-kemia patients in vivo. Results: Cytarabine induced S phase specific cell-cycle blockage and apoptosis in exponentially growing Molt-4, but showed G0 / G1 phase specificity in high -density cultured Molt-4 and in clinical specimens. Paclitaxel induced G2 / M phase specific cell-cycle blockage and apoptosis in exponential Molt-4, but showed G0 / G1 phase specificity in high-density cultured Molt-4 and S phase specificity in clinical specimens. the first day of clinical chemotherapy, cytarabine induced G0 / G1 with a little S phase apoptosis in leukemia cells of acute lymphocyte leukemia patient in vivo. Cytarabine plus paclitaxel t ogether had almost the same effect in the second day. Confc: The cell-cycle effects of cytarabine and paclitaxel were different in different target cell growing status. It should be noted that the in vivo effect of these agents may be different from often during clinical chemotherapy. The combination chemotherapeutic regimens may need to be redesigned.