Bronchoalveolar lavage (BAL) has emerged as a useful technique for the study of pulmonary interstitial disorders. Several types of information are provided by the evaluation of lavage fluid. Identification of cellular constituents helps to separate inflammatory process. Recently we have studied cellular constituents of BAL from three cases with histologically confirmed pulmonary sarcoidosis, idiopathic pulmonary fibrosis and hypereosinophilic syndrome. Pulmonary sarcoidosis showed a marked increase in lymphocytes, idiopathic pulmonary fibrosis revealed a predominance of neutrophils, and hypereosinophilic syndrome presented a marked increase in eosinophils in the lavage fluids.