Results: From 86 patients, 59 cases were exudates and 27 cases were transudates. The criterion of pleural cholesterol above 43mg/dl had sensitivity of 73.8% and specificity of 92% that with decreasing criterion level to 35.5mg/dl, sensitivity increased and reached 81.4%. Ratio of pleural fluid cholesterol to serum more than 0.3 had 65% sensitivity, 88% specificity and 85% efficiency. Ratio of pleural fluid bilirubin to serum more than 0.6 had 76.3% sensitivity, 74.1% specificity and 75.6% efficiency. Conclussion: The criterion on 3 g/dl protein still had highest sensitivity and specificity in differentiating exudate from transudate and can be used as best determinant a lone. Also pleural fluid cholesterol more than 35.5mg/dl has suitable sensitivity and specificity and the combination of pleural fluid protein and cholesterol can be used as best practical determinant. The criterion of pleural fluid cholesterol to serum ratio more than 0.3 has low sensitivity and with reduction of this radio to 0.14, its sensitivity increases but its specificity will decrease.