The diversity of the human TCR repertoire in aging has been studied by examining the profiles of complementarity-determining region 3 (CDR3) sizes expressed by the BV families. The TCRBV CDR3 profile, which shows size heterogeneity in young adult humans, is significantly restricted in aged humans. Clonal T cell expansions were identified using a PCR-based approach, in one or more BV families from all 14 healthy persons over the age of 65 that we studied. CD4+ T cell expansions were identified in 8 of 11 donors and CD8+ T cell expansions in 7 of 10 donors. These clonal expansions were stable during a 2-year period. Interestingly, more than half of the aged persons had clonal expansions within the BV3, -14, -16, and -23 families. Although there was no homology among the eight CDR3 sequences identified in clonal T cells from 8 aged persons, selective pressure on the expanded T cell clones was suggested by the fact that the BV families used by the T cell clones were not proportional to the number of genes in the different BV families.