We studied cell findings in the bronchoalveolar lavage fluid (BALF) of 13 patients with nonspecific interstitial pneumonia (NSIP) and 20 with ordinary interstitial pneumonia (UIP). NSIP and UIP were difficult to distinguish by high-resolution CT. Surgical lung biopsies were performed in all patients. We divided the patients with NSIP and UIP into 4 groups, a group of idiopathic NSIP (idiopathic NSIP), a group of NSIP patients associated with collagen vascular disease (CVD NSIP), a group of idiopathic UIP patients (idiopathic UIP) and a group of UIP patients associated with collagen vascular disease (CVD UIP). We then examined the differences in BALF cell findings between these groups. The percentage of lymphocytes in BALF was higher in idiopathic NSIP and CVD NSIP than in the healthy control. The percentage of alveolar macrophages was lower and the percentage of lymphocytes was higher in CVD NSIP than in idiopathic UIP. The CD4/CD8 ratio in BALF of idiopathic NSIP was lower than with idiopathic UIP. It is important that NSIP be distinguished from UIP clinically, and our results suggest that BALF cell findings may be useful for making this distinction.