Cellular transfer of experimental autoimmune encephalomyelitis (EAE) was effected in mice with lymph node cells (LNC) from appropriately immunized donors. Pretreatment of LNC with anti-Lyt-1 and Lyt-2,3 antibodies indicated that the transfer of both EAE and a cell-mediated immune response in vitro to MBP was dependent on a subpopulation of T lymphocytes expressing the phenotype associated with the helper and cell-mediated delayed hypersensitivity functions, Lyt-1+, 2-.