Patients with pulmonary sarcoidosis frequently have increased numbers of lymphocytes and a high ratio of CD4+ to CD8+ T-lymphocytes (CD4/CD8 ratio) in bronchoalveolar lavage (BAL) fluid. Some investigators have suggested that these parameters can be used to distinguish sarcoidosis from other types of interstitial lung disease with a high degree of reliability. However, we hypothesized that the BAL CD4/CD8 ratio measured during the initial diagnostic evaluation of patients with biopsy-proven sarcoidosis is highly variable. BAL lymphocytes were analysed via flow cytometry to determine the CD4/CD8 ratio in a population of 86 patients with histological and clinical evidence of sarcoidosis, who underwent BAL as part of their initial diagnostic evaluation. In these patients, the CD4/CD8 ratio ranged 0.5-37.3, with a median value of 3.35 (mean 6.49). The CD4/CD8 ratio was greater than 4 in only 36 (42%) subjects. Ten patients (12%) had a CD4/CD8 ratio less than 1. The distribution of CD4/CD8 ratios was similar in the presence or absence of BAL lymphocytosis. In conclusion, the CD4/CD8 ratio in bronchoalveolar lavage fluid is highly variable in biopsy-proven sarcoidosis. Bronchoalveolar lavage lymphocyte subset determination is a diagnostic test with low sensitivity for this disease.