In the present paper, it is reported that immunelogic event during unset of experimehtaleallrgic encephalomyelitis (EAE) is studied by sevaeral immunological parameters, including thymectomy at birth in Guinea Pigs, identification of various cellular and humoral immunolo-gic functions. It is observed that thymectomy at birth suppressed onset of EAE and severityof EAE is related to cellular immunologic function but not to humoral immunity. All ofthese results indicated that cell-mediated immunity is responsible for the onset of EAE.