Infection of mice and rats with any one of five tested human adenovirus types belonging to groups A and B (types 3, 7, 12, 18 and 31) induced an immunity to the TSTAs of type 12 tumors as detected by the colony inhibition (CI) test. No immunity was found against an adenovirus type 1 tumor. Two adenovirus types belonging to group C (types 1 and 5) were similarly tested and found to induce a clear‐cut immunity to the adenovirus type 1 tumor but not to tumors induced by adenovirus of groups A and B. The only tested virus type of group D (type 4) did not induce any clear‐cut immunity to either adenovirus 12 tumors or the adenovirus 1 tumor. Immunization of rats with rat adenovirus 12 tumor cells induced a cellular immunity to adenovirus 12 mouse tumor cells but not to a mouse polyoma tumor. Adenovirus 1 rat tumor cells induced no such immunity. Immunization of rats with syngenic adenovirus 12 tumor cells induced a cellular immunity to adenovirus 12 rat and mouse tumors and an adenovirus 7 hamster tumor, but not to an adenovirus 1 rat tumor or BHK‐C13 control hamster cells. The result of a tumor prevention experiment is consistent with the existence of a common TSTA induced by types 7 and 12 and a different TSTA induced by type 5 virus. It is concluded that the highly oncogenic group A and the weakly oncogenic group B adeno virus types all induce a common TSTA. Another TSTA is induced by the group C viruses, while no evidence has been obtained for the existence of any TSTA induced by a group D virus type.