In a continuation of our studies in the Friend virus (FV) system, attempts will be made to repeat in cultured cells our observations in vivo of selective incorporation of H-2 antigens into completed virions. Also, new cultured tumors cell lines of the recombinant H-2h and H-2i genotypes are being established for continued mapping studies of H-2 molecules which form antigenic complexes with viral proteins on the cell surface. However, our major emphasis will be on extending the recent findings in the FV system to the Gross virus (GV) system. Cultured, GV-induced lymphoma cell lines of our BALB/c, H-2-congenic mouse strains have been established and are being investigated for their capacity to induce T-cell immunity in syngeneic hosts. Also, GV particles collected from infectious serum and from culture supernatants will be examined for selective inclusion of H-2 antigens. We will also attempt to demonstrate the role of T suppressor cells in this system by cell separation techniques, since the unresponsiveness of mice of certain H-2 types may well be due to the appearance of such suppressor cells.