A high CD4(+)/CD8(+) ratio in bronchoalveolar lavage fluid is indicative for the diagnosis pulmonary sarcoidosis but this ratio only does not fully discriminate pulmonary sarcoidosis from other interstitial lung diseases. Recently, the integrin CD103 has been implicated in the diagnostic evaluation of sarcoidosis. CD103 is expressed on intraepithelial lymphocytes in mucosal areas, including bronchi, and is possibly involved in the retention of lymphocytes to the mucosa. The Dutch BAL working party initiated an investigation to evaluate the diagnostic value of relative number of CD103 expressing CD4(+) T-lymphocytes in the BAL fluid of patients with a variety of interstitial lung diseases. The expression of CD103 was examined on bronchoalveolar lavage cells from 119 patients including 56 patients with pulmonary sarcoidosis. We redefined criteria for alveolar CD4(+) T-cell lymphocytosis and for the relative enumeration of CD103 expressing CD4(+) T-lymphocytes in the BAL fluid. Our data demonstrate that the combined use of the CD103(+)CD4(+)/CD4(+) ratio (<0.2) and the BAL CD4(+)/CD8(+) ratio (>3) or the relative alveolitis CD4(+)/CD8(+) BAL/PB ratio (>2) provides a specific tool for discriminating sarcoidosis, also without a clear CD4(+) alveolitis, from other interstitial lung diseases.