Total sialic acid (TSA), lipid-bound sialic acid (LSA), ferritin and carcinoembryonic antigen (CEA) were evaluated in 55 patients with malignant pleural effusions and in 32 patients with benign (exudative) pleural effusions. No significant differences were found in the pleural fluid TSA, LSA and ferritin levels between malignant and benign conditions. CEA levels in malignant effusions were significantly higher than those in benign effusions (43.13 +/- 72.8 ng/ml versus 2.6 +/- 5.56 ng/ml, p less than 0.01). At a cut-off level of 5 ng/ml, 60% of the patients with cancer showed elevated pleural fluid CEA levels. The specificity and diagnostic accuracy of CEA in distinguishing malignant from benign pleural exudates were both very high (91% and 71% respectively). Therefore, of the four markers investigated, only CEA could be a valuable tool in the detection of pleural malignancy.