Immunization of CBAT6T6 mice with MC‐29 hepatoma antigen did not change the take of Rous sarcoma virus, Schmidt‐Ruppin strain [RSV(SR)] mouse tumors after sc transplantation. Immunization with MC‐29 hepatoma antigen only slightly increased the average survival time of the mice and significantly decreased tumor growth only at the minimal lethal dose level. Immunization of mice with MC‐29 hepatoma antigen and immunization with chicken Rous sarcoma gave similar results; both elicited much less transplantation resistance than immunization with irradiated RSV(SR) mouse tumor cells. The data indicate that there are common tumor‐specific transplantation antigens of MC‐29 hepatoma and Rous sarcoma, but further in vitro experiments are needed to prove this.