Two hundred and four patients with pleural effusion were studied to investigate the utility of Light's criteria and pleural fluid cholesterol level (pCHOL) in the identification of exudative pleural effusion (EPE) and transudative pleural effusion (TPE). There were 48 TPE, 56 tumor, 47 tuberculous, 30 metapneumonic and 23 miscellaneous patients. A value > or = 54 mg/dl for pCHOL and > or = 0.32 for the pleura/serum cholesterol ratio (p/sCHOL) showed sensitivity (S) and specificity (Sp) of 95.5% and 91.6% for pCHOL, and 97.4% and 91.6% for p/sCHOL, respectively. Combined pCHOL and/or p/sCHOL showed a S of 98.7% and Sp of 89.5%. Light's criteria achieved a S of 100% and Sp of 64.5%. Combined pCHOL and p/sCHOL revealed a similar accuracy to Light's criteria in EPE diagnosis but was found to be more exact in TPE diagnosis.