Anti-HTLV-II gp46 (Clone 73/4.9.8) reacts with Human T-Lymphotropic Virus Type II (HTLV-II) surface protein. This murine monoclonal antibody exhibits reactivity with viral lysates examined using Western blotting and ELISA techniques. The antibody reacts with HTLV-II infected cell lines using indirect immunofluorescence. Cross reactivity of the antibody with HTLV-I gp46 has been observed. The antibody was raised by immunizing mice with purified HTLV-II lysate. It is of the IgG1 subclass and has been purified from serum-free culture supernatant by protein A chromatography.