A 79-year-old woman with small-cell lung cancer was treated weekly with paclitaxel after previous treatment with carboplatin and etoposide. Within the first course of paclitaxel, chest radiography and CT revealed thickening of the bronchovascular bundle and interlobular septa, and infiltrates in both lung fields. A marked increase in the number of lymphocytes was found on bronchoalveolar lavage (BAL). Microorganisms such as Cytomegalovirus, Mycobacteria, and Pneumocystis carinii were absent from the BAL fluid. Interstitial infiltration was partially improved simply by stopping paclitaxel administration, without the need for any additional therapy. Drug-induced pneumonitis caused by paclitaxel was diagnosed on the basis of the clinical course and findings, although a drug lymphocyte stimulation test yielded negative results for paclitaxel. Interstitial infiltrates on imaging, symptoms and arterial blood gas results improved with administration of oral prednisolone. The possibility of pneumonitis induced by paclitaxel should be considered even in cases without interstitial lung disease.