SUMMARYAlice bearing Ehrlich ascites carcinoma show a modified immune response to primary and secondary skin allografts. The present experiments were undertaken to investigate the role of Immoral factors in cell-free Ehrlich ascites fluid (CFEAF) in the reaction between host and allograft. Administration of CFEAF did not alter rejection of primary skin allografts. However, accelerated rejection of second and third allografts was suppressed by continued administration of CFEAF. Rejection of the second and third allografts did occur, but the rejection pattern and survival time were typical of primary graft rejection. Selective inhibition of the immunological memory of the host, indicated by suppression of accelerated secondary graft rejection, taking place in the presence of a repeated and concurrent “primary” immunological response to a second allograft, suggests there is a qualitative difference between the primary and secondary immune response to cellular antigens. Further investigation of the mechanism by which CFEAF selectively suppresses the secondary immune response may lead to a better understanding of this important biological process and additionally, may provide information about the growth of tumor cells in immunologically competent hosts.