This report describes the qualitative analysis of T cell receptor (TCR) repertoire regeneration in recipients of BMT. RNA samples from patient and control peripheral blood lymphocytes were prepared and tested for the presence of multiple V alpha and V beta transcripts by the polymerase chain reaction. TCR V gene expression was highly diverse within the first 6 months post-transplantation in recipients receiving either T cell-depleted or T cell-replete marrow, and in HLA mismatched as well as matched donor-recipient pairs. The sequencing of TCR message from BMT recipients also demonstrated J gene diversity and apparently normal junctional diversity at the V-J alpha join. Thus, T cell pools in BMT recipients are largely heterogeneous, not mono- or oligoclonal.