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Background. The value of bronchoalveolar lavage (BAL) still remains controversial, prompting a need for further improvement. The purpose of this study was to develop and evaluate a sequential analysis of cell content in fractional BAL (FBAL) from the airways and alveolar sacs with incorporation of the cellular morphologic features. Methods. Initially, 30 ml saline was infused into a subsegmental lobe of the lung and the recovered fluid was assigned as FBAL-I being mainly originated from whole airways. The second and third lavages (FBAL-II and FBAL-III) each were performed using 50 ml saline being from more distal portions of airways and alveolar sacs respectively in the same lobe. Total cell number/ml and percentages of macrophages, lymphocytes, neutrophils, and eosinophils in each fraction together with their morphological alterations and mast cells, basophils and Masson bodies were assessed. Results. In the 12 controls, percentage of neutrophils was high and lymphocytes and macrophages were low in FBAL-I while in FBAL-III, neutrophils decreased to nearly nil and lymphocytes and macrophages were increased. Analysis of FBAL from 76 patients with sarcoidosis and 14 with hypersensitivity pneumonitis (HP) revealed that a predominance of small, round and well-differentiated lymphocytes with relative absence of neutrophils, basophils and Masson bodies correlated best with sarcoidosis. In contrast, neutrophil predominance and presence of lymphocytes having deep nuclear indentations and abundant cytoplasm with a process resembling a “hand-mirror” correlated well with HP. Conclusions. Evaluation of FBAL together with cellular morphological features especially characteristics of lymphocytes provides valuable information for establishing the diagnosis in interstitial lung diseases.