BACKGROUND: The purpose of this study was to evaluate the usefulness of the pleural fluid carcinoembryonic antigen (CEA) and cytokeratin fragment 19 (CYFRA 21-1) tumor markers as complementary tools for the diagnosis of malignant pleural effusions. PATIENTS AND METHODS: The levels of pleural and serum CEA and CYFRA 21-1 were prospectively assayed in 222 patients with pleural effusions (150 benign effusions, 57 bronchogenic carcinomas and 15 metastatic carcinomas). RESULTS: The levels of pleural fluid CEA and CYFRA 21-1 in the malignant effusions were significantly higher than those in the benign effusions. With a specificity of 95%, the cut off values for the CEA and CYFRA 21-1 in pleural effusions were 5 and 89 ng/ml, respectively. The diagnostic sensitivities of the pleural fluid CEA and CYFRA 21-1 in malignant effusions were 72 and 54%, respectively, whereas using a combination of the two, the sensitivity increased to 87% (p<0.05). CONCLUSIONS : These findings suggest that a combination of the pleural fluid CEA and CYFRA 21-1 in pleural effusions can be useful in the diagnosis of malignant pleural effusions.