RESULTS: In 94 cases with malignant pleural effusion, 74 patien- ts (78.7%) were adenocarcinoma. In 60 cases of pleural effusions with benign origin, 39 cases (25.3 %) were caused by tuberculosis, 13 cases (8.4 %) were caused by heart failure, 5 cases (3.2 %) were due to pne- umonia and 3 cases were attribute to hypoproteinemia. Among patien- ts under 45 years (including 45 years old), tuberculous pleuritis was major reason for pleural effusion; in patients between 46 and 60 years old and over 60 years old, most pleural effusion were finally diagnosed to be malignant pleural effusion (72.8%, 67.2%). The detection rate of carcinoma cells in exudates with blood effusion was signifycantly higher than that in exudates with non-blood effusion (P<0.05). The level of dehydrogenase (LDH) in malignant pleural effusion increased obviously and was significantly higher than the level in tuberculous pleural effusion (P<0.05). The positive incidence of cancer cell in pleural effusion was 64.2% (43/67) and 13.3% (10/75) in phlegm. The rest cases, among which 28 cases were inspected by transbronchial lung biopsy, 8 were detected by lymph follicle needle aspiration biopsy and 5 were discovered by CT-guided percutaneous needle aspiration biopsy of lung. The overall incidence of above three items was positive.