Aim of the work: To evaluate the role of interleukin-6 (IL-6) in diagnosis of malignant pleural mesothelioma by detecting its level in the pleural fluid and serum of the patient with malignant pleural mesothelioma in comparison with other causes of pleural effusion. Materials and methods: This study was conducted on 44 patients (25 males and 19 females) with pleural effusions of different etiologies, at Banha University Hospital from April 2011 to December 2012. These patients were classified according to their final diagnosis into four groups: Group I: included 20 cases with malignant pleural effusions secondary to malignant pleural mesothelioma. Group II: included 7 cases with malignant pleural effusions secondary to metastatic adenocarcinoma. Group III: included 7 cases with tuberculous pleural effusions. Group IV: included 10 cases with transudative pleural effusions. IL-6 measured in both plasma and pleural fluid of selected patients and statistically analyzed. Results: The mean values of pleural fluid IL-6 were higher among patients with malignant effusion (groups (I, II), respectively) than those with non malignant (groups (III, IV)), these differences were statistically significant (p
