The levels of soluble interleukin 2 receptor alpha (sIL-2R alpha) were measured in pleural fluid from 38 patients including 16 cases with tuberculous pleurisy, 14 with malignant pleural effusions and 8 with transudative effusions by using ELISA technique. The level of sIL-2R alpha in tuberculous pleurisy is markedly higher than in malignant pleural effusions (P < 0.01). The levels of sIL-2R alpha in tuberculous pleurisy and in malignant pleural effusions are significantly higher than in transudative effusions (P < 0.01). The clinical significance is discussed.