A major expansion of CD8+57+ lymphocytes expressing an alpha-beta T- cell receptor (TCR) is frequent after bone marrow transplantation (BMT). We examined the clonality of the TCR beta gene repertoire in these expanded CD8+57+ cells after allogeneic or autologous BMT. We performed a polymerase chain reaction (PCR) analysis of the V beta chain usage in CD8+57+ cells purified from nine BMT recipients with a series of oligonucleotides specific for 20 V beta gene families. PCR products from selected TCR beta gene rearrangements were sequenced. The CD8+57+ cells from eight of nine patients used a restricted set of V beta families, with a marked predominance of two to three V beta gene families per patient, whereas the control autologous CD57- subset expressed the whole 20 V beta families. A direct sequencing analysis confirmed the V beta 16 and V beta 17 clonality in six patients, showing a striking homology in the CDR3 sequences of the V beta 16 products. The CD8+57+ cells, but not the CD57- cells, displayed an oligoclonal pattern of TCR rearrangements as shown by PCR analysis of TCR gamma gene rearrangements. Such an oligoclonal expansion of CD8+57+ cells, using a restricted set of the V beta gene families, may result from a specific TCR stimulation of a limited number of T-cell clones in BMT recipients.