Twenty identified cytokeratins form a complex family of intermediate filaments. Cytokeratin 5 (58 kDa) & cytokeratin 6 (56 kDa) are high molecular weight type II keratins expressed in a variety of normal tissues including breast, prostate, mesothelium, skin and esophagus. Anti-Cytokeratin 5 & 6 is a useful immunohistochemical marker in the identification of mesothelioma and lung epithelial carcinoma. In combination with 34bE12 and P504S it can help in the diagnosis of benign and malignant prostate lesions.