To assess the value of transbronchial lung biopsy in the evaluation of disease activity in pulmonary sarcoidosis, lung biopsy specimens obtained from 37 patients with this disease and their cellular patterns of bronchoalveolar lavage were studied. Morphologic analysis has showed peculiar lesions: predominant interstitial alveolitis consisting of mononuclear cells and scattered neutrophils, and eosinophils, diffuse in 13 cases and focal in 11 cases, interstitial nodular clusterings of mononuclear cells (five cases), diffuse intraalveolar infiltration of macrophages (one case), granulomas (27 cases), hyaline membranes (one case), intraalveolar (two cases) and interstitial (six cases) fibrosis, and finally cuboidal metaplasia of alveolar lining cells (eight cases). Hyaline membranes were always combined to a diffuse alveolitis consisting of some neutrophils. Only diffuse alveolitis was significantly associated with a high lymphocytosis in BAL (p less than 0.05).