Previous work showed that mice that had been thymectomized at 3 days of age tended, in later life, to develop a hyperplastic autoimmune gastritis and were also hypersusceptible to sarcogenesis by low dosages of 3-methylcholanthrene. In the present work, it was found that the hyperplastic autoimmune gastritis could be transferred with great efficiency with spleen cells obtained from 3-mo-old donors that had been thymectomized at 3 days of age, but which had not, at the time of transfer, themselves developed overt disease. The recipients were 1-mo-old syngeneic mice that had been made receptive by thymectomy during the first day of life, a procedure that does not, of itself, cause autoimmune disease. The high efficiency of the transfer suggests that, during the transfer process, effector cells may have been differentially favored as compared with the suppressor cells that, in normal animals, supposedly prevent autoimmunity. The practicality of the transfer technique should permit an investigation of the cellular basis of the autoimmunity and the associated increased susceptibility to low-dose hydrocarbon sarcogenesis.