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A tumor antigen capable of inducing tumor resistance (tumor rejection antigen; TRA) was obtained in a solubilized form by sodium dodecyl sulfate (SDS)-extraction of plasma membrane fraction from Rous sarcoma virus (RSV)-induced CSA1M fibrosarcoma cells (BALB/c origin). Analyses by Sephacryl S-300 gel filtration and SDS-polyacrylamide gel electrophoresis revealed that TRA activity was recovered in the fraction of an approximate molecular weight (m. w.) of 60kD. Such TRA was also found to exist in plasma membrane fraction from various RSV-induced tumor cells but not from tumor cells induced with agents other than RSV. Unfractionated crude SDS-solubilized preparation contained gp 70 as detected by rabbit anti-gp 70 antiserum, whereas this reactivity was lost in the fraction exhibiting an m.w. of about 60 kD. Since this fraction retained pp60src activity, the relation of TRA to pp60src was further investigated. pp60src was also obtained from the lysate of v-src-expressing yeast transformant. Immunization of BALB/c mice with such pp60v-src-containing lysate failed to induce any significant tumor protection. The above 60 kD fraction of CSA1M solubilized antigens was allowed to bind to Sepharose beads coupled with anti-pp60src monoclonal antibody and was depleted of pp60src. Immunization with the fraction depleted of pp60src activity (bead-unbound fraction) resulted in potent tumor protection. These results indicate that the CSA1M solubilized membranous component(s) which has an approximate m.w. of 60kD but is (are) distinct from functional pp60src functions as the TRA against RSV-induced CSA1M tumor cells. The results are discussed in the context of (1) the relationship between the src gene and the expression of TRA and (2) genetic control in immune responses to the TRA common to RSV-induced tumor cells.