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To determine the levels of the tumor markers carcinoembryonic antigen (CEA), cytokeratin 19 fragment (CYFRA21-1) and carbohydrate antigen 15-3 (CA 15-3) in the blood and pleural fluid of patients with benign or malignant pleural effusion, evaluating the sensitivity of each marker in these fluids.We prospectively evaluated 85 patients with pleural effusion. The study of the pleural fluid observed the criteria established in the literature. Levels of the markers were determined using electrochemiluminescence. The sensitivity was determined on the condition that the specificity wasor = 90%.Of the 85 cases, 36 (42.4%) were malignant, 30 (35.3%) were benign, and the results were inconclusive in 19 (22.3%). In the malignant cases, the CEA and CYFRA21-1 levels were higher in the pleural fluid than in the blood, which was not observed for CA 15-3. In the benign cases, the CYFRA21-1 levels were higher in the pleural fluid than in the blood, whereas the opposite was found for CEA and CA 15-3. There were significant differences between malignant and benign cases for all markers, in pleural fluid and blood. In the pleural fluid, the sensitivity of CEA, CYFRA21-1 and CA 15-3 was 69.4, 69.4 and 66.7%, respectively, and the combined sensitivity was 80.6%. In the blood, the sensitivity was 57.1%, 71.4% and 48.6% for CEA, CYFRA21-1 and CA 15-3, respectively, and the combined sensitivity was 77%.The results suggest that these markers might be useful in the differentiation between malignant and benign pleural effusion.