Findings of bronchoalveolar lavage fluid (BALF) were compared among three groups of patients: rheumatoid arthritis (RA) with or without interstitial lung disease (ILD), and collagen disease other than RA accompanied by ILD. Regardless of the presence or absence of associated ILD, the RA groups showed higher numbers of neutrophils in BALF with a mean number about 10 times that of the collagen disease group. In contrast, the percentages of lymphocytes in the RA groups were lower than that in the collagen disease group. Classification of alveolitis on the basis of BALF findings revealed neutrophil type (N) in 55% of the RA patients and lymphocyte type (L) in 25%. In the collagen disease group, N was found in 15.4%, and L in 38.5%. Regarding the lymphocyte subsets, many patients with RA accompanied by ILD had a CD 4/8 ratio of 1 or great. These findings suggest that highly characteristic neutrophil alveolitis is present in the pulmonary interstitium from the initial stage of RA.