Cell recipients which have recovered from adoptively transferred Experimental Allergic Encephalomyelitis (EAE) mediated by encephalitogenic T-cell lines do not develop clinical disease following subsequent challenge with myelin basic protein (MBP) emulsified in CFA (MBP-CFA), a recipient response termed vaccination. The immune mechanism(s), which accounts for the vaccination-induced resistance response, is not known. We have used an adoptive transfer system to investigate the point@) of control within the pathway of EAE effector cell development from MBP-specific naive precursors that prevents clinical disease in T-cell line vaccinated, MBP-CFA challenged Lewis rats. Although EAE effector cells do not develop in T-cell line vaccinated recipients, our data shows that MBP precursor cells are primed in T-cell line vaccinated MBP-CFA challenged animals, and these MBP-specific precursor cells can be stimulated in culture to the EAE effector cell level. MBPmemory cells also arise in T-cell line vaccinated MBP-CFA challenged donors, as demonstrated by the early and rapid onset of EAE in MBP-CFA challenged recipients of lymphnode cells from T-cell line vaccinated MBP-CFA challenged donors. We also found that it was possible to adoptively transfer resistance to MBP-CFA challenge using spleen cells from donors previously vaccinated with encephalitogenic T-cells. These results show that although EAE effector cells do not develop in T-cell line vaccinated animals, T-cell vaccination does not inhibit the initial MBP precursor cell response and does not prevent the development of MBP memory cells.