The goal of this study is an understanding of the relative influence of the various factors governing lymphomagenesis in the C57 BL mouse which carries a leukemogenic virus (RAd LV) from embryonic life but has a normally low incidence of lymphoma and leukemia. The achievement of this goal will require clarification of (1) the mode of natural transmission of the virus, (2) the basis of latency of the infection and (3) the mechanisms affecting lymphomagenesis by the virus, by irradiation and by other potentiating agents. An attempt will be made to modify the vertical transmission of the virus by immunization and by superinfection of the parents prior to mating. The presence of DNA homologous to the viral RNA will be sought in the tumors and normal tissues of the mouse by hybridization. The effect of irradiation and chemical perturbation of cells on incorporation of the viral genome will be tested similarly. Derepression of the viral genome by these means will be judged by virogenesis, appearance of new cell surface antigens and transformation. The relative roles of immunosuppression and immunological enchancement in lymphomagenesis will be assessed.