The therapeutic effect of steroid hormone(STH) against pulmonary fibrosis was evaluated in 6 patients with dermatomyositis(DM), 6 with progressive systemic sclerosis(PSS), 3 with rheumatoid arthritis(RA) and 5 with idiopathic pulmonary fibrosis(IPF). Of these patients, 7 were male and 13 were female. The average age was 46.5, ranging from 24 to 66 years old. Dosage of STH varied between 10mg and 40mg/day in each patient and the mean administration period was 14 months. Clinical effects were determined using chest X-ray film, % VC, PaO(2) and direct questioning. Twelve out of 20 patients improved after STH therapy. The clinical effectiveness of STH depended on the ground disease of patients with pulmonary fibrosis; that is, STH was most effective against pulmonary fibrosis in patients with DM and less effective in patients with PSS. STH was also effective in patients with acute stage IPF, but not in patients with chronic IPF. STH seemed to be dose dependent, being more effective in patients with the high dosage of STH. Nodular shadows on chest X-ray film were more sensitive to STH therapy than reticular shadows. Moreover, % VC and PaO(2) seemed to be useful for judging the effectiveness of STH therapy.