A 23-year-old man was admitted to the hospital because of non-productive cough, slight fever and generalized lymphadenopathy. Chest roentgenogram showed bilateral hilar and paratracheal adenopathy, diffuse granular infiltrates and right subpulmonary effusion. Pleural aspiration yielded 180ml of clear yellow fluid with a specific gravity of 1.039 and protein content of 3.83g/dl with 80% lymphocytes. The T cell subsets analysed by FACS using monoclonal antibodies showed significantly greater percentage of Leu 3a cells in pleural fluid (73%) than in peripheral blood (28%). ACE in pleural fluid was also elevated. Smears and cultures for acid-fast bacilli and fungi were negative. A pleural biopsy obtained with a Cope needle showed multiple non-caseating granulomas. Prednisone therapy resulted in rapid disappearance of the pleural effusion, progressive clearing of diffuse granular infiltrates and lymphadenopathy.