In a trial to evaluate the role of lipids in differentiation between transudative and exudative pleural effusions, the present study was conducted on 50 patients with clinical and radiological evidence of pleural effusion. Patients were classified into 2 groups: Group 1 (transudates of 21 patients) and Group 2 (exudates of 29 patients). It was found that pleural fluid cholesterol and pleural fluid/serum cholesterol ratio is a valuable aid in differentiation between transudates and exudates. Applying a combination of pleural fluid cholesterol (cut-off 60 mg/dl) and/or pleural fluid/serum protein ratio (cut-off 0.5) may prove superior to Light's criteria.