A late phase II clinical study of RP56976 (Docetaxel) was conducted in patients with non-small cell lung cancer. Patients with non-small cell lung cancer in Stage IIIB and Stage IV not previously treated were enrolled. Docetaxel was administered at a dose of 60 mg/m2 based on the results of a phase I and an early phase II clinical study, and the efficacy and safety were examined. Of the 77 patients enrolled, 72 patients were evaluated to have completed the scheduled course of treatment by the Evaluation Committee. A partial response (PR) was seen in 18 patients, and the overall response rate was 25.0%. The response rate classified by clinical stage was 28.0% (7/25) in patients with Stage IIIB and 23.4% (11/47) in patients with Stage IV. Hematological adverse reactions included leukopenia of Grade III or more in 53.3% (40/75) and neutropenia of Grade III or more in 86.7% (65/75) as specified in the Adverse Event Reporting Form proposed by the Japan Society for Cancer Therapy. Other major adverse reactions included alopecia, asthenia, and fever, all of which were tolerable. From these results, the efficacy of docetaxel for the treatment of non-small cell lung cancer was confirmed.