[en] Experimental autoimmune encephalomyelitis (EAE) can be induced in Lewis rats without the use of adjuvant. Spleen cells of naive rats were sensitized to myelin basic protein (MBP) in vitro. Transfer of these cells did not result in the development of EAE. However, spleen cells from primary recipients, taken 10 days post transfer, and cultured with MBP (secondary culture, transferred EAE to secondary recipients. EAE can be induced in primary recipients by the transfer of secondary cultured cells or cultured cells or challenge with MBP in complete Freund's adjuvant (CFA) or incomplete Freund's adjuvant (IFA) 10 days after injection of naive cultured cells. The finding that MBP-CFA challenged 1' recipients developed EAE, suggests that the rats have been primed to MBP through the naive cultured cell transfer. The cells from naive culture that sensitize the primary recipient were radioresistant (1500 R), probably macrophages. This is in contrast to the cells transferring EAE to the secondary recipient, which were radiosensitive. Unlike the spleen cells which transfer EAE from MBP-CFA sensitized rats, the cells in the secondary transfer could not be activated to transfer EAE when cultured with concanavalin A. Clinical EAE in the secondary recipient was more severe when these rats were irradiated (200 R) prior to transfer. There is evidence that low dose irradiation eliminates naturally occurring suppressor cells. EAE also developed in lethally irradiated (850 R) recipients of secondary cultured cells, suggesting that the transferred cells can induce EAE alone or by recruiting radioresistant cells in the secondary host