BACKGROUND: The estimation of ADA activity in pleural fluid has been proved useful tool in the diagnosis of tuberculous pleural effusions. However, there is controversy about its usefulness when estimated in bronchial washing fluid in the patients with pulmonary tuberculosis. This study aims at evaluating the usefulness of measuring ADA activity in bronchial washing fluid of tuberculous patients as biochemical marker in the early diagnosis of the disease. METHODS: We examined the difference of ADA activity in bronchial washing fluid among the group I (tuberculosis group), group II (lung cancer group) and group III (control group). RESULTS: There was significantly higher bronchial washing fluid ADA level in tuberculosis group compared to the lung cancer and control groups(p<0.01). CONCLUSION: These results suggest that bronchial washing fluid ADA activities seem to be a useful tool in the diagnosis of pulmonary tuberculosis.