We monitored the therapeutic drug paclitaxel (Zisu) and studied its anticancer activity and side effects in 11 cancer patients. After intravenous infusion of 135 to 185 mg/m2 of paclitaxel, Cmax ranged from 2.17 to 9.17 mg/L and AUC ranged from 4.37 to 16.01 mg/h/L. A significant individual difference in pharmacokinetic parameters was found. Among the 11 patients, 6 achieved a partial remission and one patient had a mild response. The Cmax of the patients who achieved PR and MR was higher in comparison to the patients with no response. In 4 of the 6 PR patients, Cmax was above 4.38 mg/L. In four of the NR patients, Cmax was equal to or below 4.04 mg/L. These results suggested a relationship between Cmax and the cancer response rate. No significant relationship could be found between Cmax and the nadir of the white blood cells and platelets.