Although the current dogma of T cell recognition stresses its exquisite specificity, T cell clones selected for a given peptide can recognize other sequentially or structurally related peptides. Here, we have examined the immunogenicity and tolerogenicity of various self-peptides derived from region 61-80 of different MHC class I proteins co-expressed in the same mouse. Following immunization of B10.A mice (K(k), A(k), E(k), L(d), D(d)) with self-L(d) 61-80 peptide, vigorous MHC class II-restricted T cell proliferation was elicited after restimulation with either the immunogen or with self-K(k) 61-80 but not with self-D(d) 61-80. Furthermore, adult B10.A mice, tolerized with L(d) 61-80 prior to immunization with L(d) 61-80 did not respond to challenge with L(d) 61-80 and the cross-reactive K(k) 61-80. However, following K(k) 61-80 immunization, L(d) 61-80-tolerized mice responded to K(k) 61-80 but not to L(d) 61-80. Thus, tolerance induction to L(d) 61-80 resulted in the elimination/inactivation of L(d) 61-80-reactive T cells including the subpopulation that cross-reacted with K(k) 61-80. However, T cells that recognized K(k) 61-80 exclusively were preserved. Moreover, we showed that immunization with K(k) 61-80 resulted in tolerance breakdown to the cross-reactive, dominant self-peptide D(b) 61-80 in B10.A(4R) mice (K(k), A(k), L(d),D(b)). Together, these results show that the autoimmune T cell repertoire is influenced by the concomitant recognition of different cross-reactive self-peptides within the same individual.