A number of recent reports have established that oligoclonality and/or clonal expansion is a common feature of the CD8+ T cell population. Oligoclonal expansion has also been observed in bone marrow transplant recipients and rheumatoid arthritis patients, disease states in which CD57+CD8+ T cells are occasionally elevated. In this study we have compared the TCR repertoire of the CD57+ and CD57- subsets of CD8+ T cells in normal persons by using three-color FACS analysis with a panel of 16 mAbs specific for TCR V segments. The CD57 surface marker was highly variable in frequency but generally present on a minority of CD8+CD3+ T cells (mean 16.3%, SD 12.7) in a group of 41 normal volunteers. Dramatic oligoclonal expansion was present in the CD57+CD8+ T cell population in 15 of 41 (37%) of our study population and thus is a characteristic feature of the normal immune system. No such prominent oligoclonal expansions were observed in the CD57-CD8+ subset, although preliminary experiments suggest that oligoclonality per se is occasionally present at a lower frequency in CD57- cells. The reasons for this persistent accumulation of oligoclonal CD8+CD57+ T cells and their function in immune homeostasis are unclear.