This MAb reacts with a 58kDa protein identified as vimentin. It shows no cross-reaction with other closely related intermediate filament proteins (IFP s) such as desmin, keratin, neurofilament, and glial fibrillary acid protein. Anti-vimentin alone is of limited value as a diagnostic tool; however, when used in panels with other antibodies, it is helpful for the sub-classification of a given tumor. Expression of vimentin, when used in conjunction with anti-keratin, is useful when distinguishing melanomas from undifferentiated carcinomas and large cell lymphomas. All melanomas and Schwannomas react strongly with anti-vimentin. It labels various mesenchymal cells, including melanocytes, lymphocytes, endothelial cells, and fibroblasts. Non-reactivity of anti-vimentin is often considered more valuable than its positive reactivity since a few tumors do not contain vimentin, e.g., hepatoma and seminoma. Anti-vimentin is also useful as a tissue process control reagent.