Pulmonary lesions appearing in chest X-ray films were studied in 24 patients with progressive systemic sclerosis(PSS), 25 with polymyositis and dermatomyositis(PM-DM), 30 with rheumatoid arthritis(RA), 37 with Hashimoto's thyroiditis(HT), 59 with Sjogren's syndrome(SS) and 18 with Behcet's syndrome(BS). Pulmonary fibrosing changes were most common in these patients. The incidence of pulmonary fibrosis in connective tissue disease was as follows: 17 patients(71%) in PSS, 16(64%) in PM-DM, 17(57%) if RA, 10(26%) in HT, 23(39%) in SS and 2(11%) in BS. Pulmonary emphysema was observed in 2 patients with SS and pulmonary infarction was observed in one patient with BS. Fibrotic changes were most severe in PSS, in which positive anti-lung antibody and involvement of the alimentary tract were ofen detected in patients with pulmonary fibrosis. Pulmonary fibrosis in DM correlated well with the titer of anti-lung antibody, but not with other laboratory findings such as anti-nuclear antibody, CH50, RF, CRP, transaminase, LDH or γ-globulin level. In RA, HT, SS and BS, there was no significant correlation between pulmonary fibrosis and the laboratory findings.