An early phase II clinical study of RP56976 (Docetaxel), a new anticancer agent of plant origin, was conducted in patients with primary pulmonary cancer as a multicentered study involving 28 Japanese institutions. Docetaxel was administered at an intravenous dose of 60 mg/m2 based on the results of a phase I clinical study, and efficacy and safety were examined. Of the 65 patients enrolled, 57 patients were evaluated to have completed the scheduled course of treatment by the Evaluation Committee. The antitumor effect in patients with non-small cell lung cancer was 21.4% (9/42). In patients not previously treated, the antitumor effect was 30.0% (6/20), in patients previously treated the antitumor effect was 13.6% (3/22), and in 13.3% (2/15) of patients with small cell lung cancer. This shows that docetaxel had an efficacy for non-small cell lung cancer. Hematological adverse reactions included leukopenia and neutropenia of Grade III or more as specified in the Adverse Event Reporting Form proposed by the Japan Society for Cancer Therapy in 53.3% (32/60) and 78.3% (47/60) patients, respectively. Other major adverse reactions included alopecia and anorexia. Neurological symptoms developed at a low frequency and were mild in severity.