The clinical features of 24 patients with non-specific interstitial pneumonia (NIP) were evaluated. The patients consisted of seven men and 17 women, with a median age of 60 years. In seven patients, the disease was idiopathic and eight had collagen vascular diseases. Cough, dyspnoea and fever were frequently observed. The time interval between the onset of symptoms and open lung biopsy was 3 months. Mild increases of IgG, CRP, and LDH were also frequently observed. The average per cent VC was 65.1 +/- 3.2% and the average PaO2 was 71.3 +/- 2.4 Torr. Bronchoalveolar lavage was done in 20 patients, and a moderate increase in lymphocytes (27.8 +/- 6.7%) with a low CD4/CD8 ratio (0.86 +/- 0.22) was observed. Multiple patchy infiltration or diffuse interstitial shadows, located predominantly in the lower fields of both lungs were the characteristic chest CT findings. Lung biopsies in this group were characterized by varying proportions of chronic interstitial inflammation and fibrosis which was temporarily uniform. Patients were given steroid pulse therapy or oral steroids. The results were mild to marked improvements in chest roentgenographic findings and lung functions. Four patients (16.7%) died because of respiratory failure caused by NIP. This is the first report to describe clinical features of NIP since the original report by Katzenstein and Fiorelli.