The induction of specific immunologic tolerance and its transfer has been studied in the in vitro response of unprimed rabbit spleen cells to solubilized phage antigens. Evidence presented shows that only viable cells transfer tolerance and that the responsible cells appear devoid of membrane-bound antigen but are sensitive to anti-thymocyte serum. It appears, therefore, that although the in vitro response to solubilized S-T2 has no demonstrable requirement for T “helper” cells, it is subject to the action of T “suppressor” cells.