We describe a case of interstitial pneumonitis associated with polymyositis who responded well to cyclosporine therapy. In October, 1993, a 49-year-old female was admitted to our hospital because of fever, muscle weakness and progressive dyspnea. Interstitial pneumonitis with polymyositis was diagnosed and daily oral steroid therapy was started. As the therapy was ineffective, pulse intravenous steroid therapies followed by oral cyclophosphamide and steroid therapy was given. Whereas serum levels of muscle enzymes decreased, she became progressively hypoxemic. No effect was observed in series of therapy including additional pulse steroid therapy, pulse intravenous cyclophosphamide therapy, oral azathioprine and oral bethametazone therapy. In April, 1994, oral cyclosporine was started. After daily oral cyclosporine was combined with steroid, her symptoms, chest X-ray, chest CT and pulmonary function tests significantly improved. Her disease became stable and there was no signs of recurrence since then. It is suggested that cyclosporine is useful for the treatment of progressive interstitial pneumonitis associated with polymyositis.