Investigate the finding that a polymorphic gene or genes, linked to the H-2 complex in mice, determines susceptibility to primary sarcoma induction following neonatal injection of RSV-containing chicken tumor material. The mechanism of action of these genes and determination of whether differences in immune response to tumor antigens are involved will be investigated, as well as exploration of the finding that both dominant and recessive resistance exists. Tests will be done to discover whether immune surveillance and/or immune stimulation is involved.