Anti-Kveim monoclonal antibody. New monoclonal antibody reacting to epithelioid cells in sarcoid granulomas. A monoclonal antibody to the sarcoid granulomagenic agent contained in Kveim suspension was prepared by immunizing mice with Kveim suspension. One monoclonal antibody (IHY-1) that reacted with the epithelioid cells in sarcoid granulomas on immunoperoxidase technique was selected. The immunoperoxidase technique was used to compare this monoclonal antibody's binding to sarcoidosis- or tuberculosis-affected lymph nodes. IHY-1 is a monoclonal antibody of IgM class. This antibody did not react to erythrocytes, lymphocytes, monocytes, alveolar macrophages, or the macrophage-derived cell lines such as U-973 and KG-1. It reacted to granuloma epithelioid cells of sarcoidosis-affected lymph nodes. The monoclonal antibody also reacted positively to epithelioid cells in tuberculous granulomas although the reaction was not as strong. Since IHY-1 was found to bind to both types of granulomas, this suggests that the epithelioid cells in sarcoidosis have antigenicity common to the epithelioid cells in tuberculosis. 