Immunohistochemistry is a powerful technique that has become an integral and essential tool of the diagnostic surgical pathologist. This course will present the state of the art of diagnostic immunohistochemistry, taking a practical but comprehensive approach utilizing an unknown case format. First there will be an introduction highlighting methodological issues and caveats in interpreting immunohistochemical studies. Following this will be presentations on applications of immunohistochemistry to diagnostic problems in surgical pathology, including; (a) characterization of large cell, undifferentiated malignant neoplasms; (b) determination of primary site of carcinomas presenting as metastases; and (c) distinction of mesothelioma from adenocarcinoma. A syllabus will be distributed at the course. After the meeting, all registrants will be mailed a CD containing all the projected material. (Last Scheduled Presentation)