Abstract: The mice inoculated with CG sarcomas or SC sarcomas and then given sub- cutaaeaus injections of tumor-specific syngeaeic liver RNA demonstrated significant inhibition of tumor dev;lopment when compared with mice which received tumor cells and then given subcutaneous injections of physiological saline.The active liver RNA preprations treated with RNAase abolished this response, Specificity for the tumor used to immunize the mice was demonstrated in that the CG-RNA prepara- tions induced immunity to CG-sarcoma syngrafts but failed to inhibit syagrafts to SC-sarcomas Whereas SC-RNA preparations induced immunity to SC-sarcoma syngrafts but not to inhibit syngrafts to CG-sarcoma. The tumor inhibitory effects of the liver RNA extracted from normal mice were nonspecific, weak and statistically nonsignificant,