The value of CEA and AgNOR in the differential diagnosis of reactive mesothelial hyperplasia, malignant mesothelioma and metastatic adenocarcinoma in plevral biopsies. The diagnostic distinction between malignant pleural mesothelioma, reactive mesothelial proliferation and metastatic adenocarcinoma is often difficult in pleural biopsies. Eighty cases with diagnosis of malign mesothelioma (54 cases), reactive mesothelial proliferation (18 cases), metastatic and peripheral adenocarcinoma of lung (8 case) seen at the Department of Pathology, Medical School of Cumhuriyet University between January 1992 June 1998 were respectivety, reviewed. CEA and Ag-NOR were used to differantial diagnosis; but Ag-NOR method can be used as an economic, easily appliable supplementary method in pleural biopsies.