Superantigens have the ability to stimulate a subset of T cells based upon their expressed TCR beta-chain. It has been demonstrated that the administration of staphylococcal enterotoxin B (SEB) in mice leads to unresponsiveness in V beta 8+ T cells in vivo which are the same T cells that could be stimulated in vitro by this enterotoxin. We present here data on the effect of SEB administration in DBA/2 and (PL/J x SJL)F1 mice on their T cell response to two different T cell determinants, the responses against which are dominated by the use of V beta 8+ T cells. Treatment of mice with SEB not only diminished their primary T cell proliferative response to these determinants, but also was able to effectively reduce the memory T cell response. SEB treatment, however, showed only a modest effect in preventing Ac 1-11-induced experimental autoimmune encephalomyelitis in H-2u mice.