Abstract: A carcinoembryonic antigen （CEA） enzyme immunoassay test was used to estimate its value in the differential diagnosis of malignant and non-malignant pleural effusions. Paired pleural fluid and serum CEA determinations were performed in 82 patients,50 50 among them with malignant and 32 with nonmalignant pleural disease.The CEA values of pleural fluid and serum of patients with malignant diseade were higher than those of patients with non-malignant.The results of this study suggest that the determi- nation of pleural CEA is of value in the differential diagnosis of malignant and non- malignant pleural effusions.