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(2), 155-160-The autologous transplantation of methylcholanthrene (MCA)-induced sarcomas in non-inbred rats, which had been immunized intensively with various allogeneic tumors, was inhibited in 33 out of 65 cases tested. The differ ence of tissues from which allogeneic tumors originated did not influence the inhibitory effect on autotransplantation. In 10 out of 69 non-immunized controls, the autotransplantation of MCA-induced sarcomas proved to be negative. In addition, remarkable lymphoid cell infiltration was demonstrated in most of tumors induced by MCA in non-inbred rats which were immunized intensively with allogeneic tumors. The autologous transplantation was more markedly inhibited in the tumor infiltrated with massive lymphoid cells than in that not infiltrated.-autologous transplantation; cross-immunity; lymphoid cell infiltration The final proof of the immunological response of the organism to the tumor itself, which had been a focus of discussion for a long time, was obtained by Klein et al. (1960), who demonstrated that resistance could be induced in the autochtho nous mouse immunized against its own MCA-induced tumor. Additionally, Usubuchi et al. (1962) found resistance to autologous transplantation of MCAinduced sarcomas in a few non-inbred rats by means of repeating the surgical removal and the autotransplantation.Then, Takeda et al. (1966) succeeded in the inhibition of autotransplantation of MCA-induced sarcomas in inbred rats after inducing the immunity due to the ligation-and-release procedure.But, if cross-immunity among syngeneic or allogeneic tumors cannot be established, the theoretical rationale for practical application of tumor immunity does not exist. Prehn and Main (1957) bad already reported some cross-immunity among syngeneic tumors induced by MCA. So Prehn (1961) attempted to inhibit MCA-careinogenesis by using the cross-immunity, but the results were completely negative against his expectation. Failure of immunization against tumorigenesis

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