A multicenter phase I clinical trial of RP 56976 (docetaxel), a new anticancer drug, was performed with single and repeated doses. Based on the results of phase I clinical trials conducted in the United States and Europe, the starting dose was 10 mg/m2. The dose was subsequently increased to 20, 50, 70 and 90 mg/m2. A dose of 60 mg/m2 was additionally tested. Single administrations of the six dose levels were performed in a total of 27 patients via intravenous drip infusion over one hour. Ten of the patients subsequently received repeated doses at three of the dose levels in the same manner. The dose limiting factor (DLF) of docetaxel is leukopenia (especially, neutropenia). Based on the observation of the DLF, the maximum tolerated dose (MTD) was determined to be 70-90 mg/m2. The white blood cell count reached a nadir about 9.5-19.5 days (median) after administration, and took 7-11 days (median) to recover. Other adverse reactions observed were nausea/vomiting anorexia, alopecia, diarrhea, fatigue and fever, which were all acceptable. The results of this trial suggest that a dosage regimen of 60 mg/m2 at 3- to 4 week intervals is appropriate in an early phase II clinical trial.