Tuberculous pleurisy is a good model for resolution of local cellular immunity. It would be expected that tuberculous pleural fluid contains a variety of immunologically important cytokines because of the accumulation of immunocompetent cells in the pleural cavity. We studied interleukin 1 (IL-1), interleukin 2 (IL-2), and interferon gamma (IFN-gamma) levels in pleural fluid of 20 patients with tuberculous pleurisy and compared them with those in pleural fluid of 20 patients with malignant pleurisy. We also evaluated adenosine deaminase (ADA) levels in both effusions. Tuberculous pleural fluid had higher levels of IL-1, IL-2, IFN-gamma, and ADA than malignant pleural fluid. Although the difference of IL-1 level between tuberculous and malignant pleural fluid was modest, that of IL-2, IFN-gamma, and ADA was dominant. These findings suggest that activated T lymphocytes in tuberculous pleural fluid concern the production of lymphokines at the morbid site and they effectively exert local cellular immunity through the action of such lymphokines.