Abstract To determine the efficacy of cyclosporin A (CysA) for the treatment of steroid-resistant interstitial pneumonitis (IP), we enrolled 25 patients with various rheumatic diseases and steroid-resistant IP in a pilot study [4 patients with rheumatoid arthritis (RA), 2 with systemic lupus erythematosus (SLE), 11 with polymyositis/dermatomyositis (PM/DM), 4 with systemic sclerosis (SSc), 1 with mixed connective tissue disease (MCTD), 3 with Sjögren syndrome (SS)]. Twelve patients (48%) showed a persistent response to CysA therapy, and 7 of them had PM/DM, including so-called amyopathic DM. Patients with a persistent response had moderately elevated lactate dehydroxygenase (LDH) levels, whereas patients who died had much higher LDH levels and hypoxia. Even patients with low blood levels of CysA achieved a persistent response. In responding patients, the symptoms, chest X-ray findings, arterial oxygen tension, and LDH level all improved after less than 4 weeks. In conclusion, CysA seem to be useful for treating patients with steroid-resistant IP, whose duration is short and severity is mild.