Up to 75% of 2,4,6-Trinitrophenyl (TNP)-self-specific helper T cells from normal BALB/c mice share a clonotypic determinant with the anti-TNP myeloma protein MOPC 460, recognized by the monoclonal antibody F6(51). Immunization of adult BALB/c mice with the MOPC 460 idiotype (Ab2 mice) leads to high titers of circulating anti-idiotypic antibodies but has no influence on the expression of the T cell clonotype. In contrast, TNP-self-specific helper cells prepared in progenies from Ab2 females, or in BALB/c mice treated as neonatals with anti-idiotypic antibodies, fail to express the corresponding T cell clonotype when immunized as adults. These results demonstrate the idiotype-dependent selection of T cell repertoires early in life and their stability in adults.