Local cellular immune responses may affect presentation and outcome in tuberculosis (TB). To investigate this hypothesis, we performed bronchoalveolar lavage (BAL) on 30 patients with untreated pulmonary tuberculosis and assessed the type of cellular inflammatory response and cytokine production. We then correlated BAL findings and cytokine production with clinical findings. We also performed BAL on a subset of patients to examine changes in cytokine production by BAL cells over time. We found that at presentation patients with less clinically and radiographically advanced TB (smear-negative, noncavitary disease) had a local immune response characterized by a predominance of lymphocytes. Furthermore, BAL cells from these patients secreted interferon (IFN γ ), and not Interleukin-4, suggesting a Th 1-type lymphocytic response. In patients with smear-positive and/or cavitary disease, macrophages or polymorphonuclear leukocytes were the predominant BAL cell type, but with treatment and clinical improvement these patients went on to recruit IFN γ producing cells to the lung. We conclude that the type of cellular immune response that occurs locally in the lung may affect presentation and outcome in pulmonary TB, and an understanding of the development of this response may lead to insights into pathogenesis and novel therapies for TB.