T-cell receptor Vss gene repertoire and clonality have been studied in patients with leukemia and solid tumors, by assaying the CDR3 size of TCR genes, using RT-PCR and genescan analysis. Few studies have studied leukemia-associated oligoclonal expanded T-cells in leukemia, therefore, the aim of this study was to investigate the distribution and clonal expansion of T-cell receptor, Vss subfamily T-cells in patients with acute promyelocytic leukemia (APL) with t(15;17). The CDR3 of TCR Vbeta24 subfamily genes were analyzed in peripheral blood mononuclear cells from 17 cases with PML-RARalpha+ APL using RT-PCR and genescan technique. Ten normal individuals served as controls. The results showed that the number of expressed Vss subfamilies (from 2 to 21 subfamilies) varied in different patients with APL. The most frequently expressed Vss subfamilies were Vbeta2 (64.7%), Vbeta15 (58.8%), Vbeta3 and Vbeta5 (47.1%), with a lower expression rate found in Vbeta11 and Vbeta20 (11.7%). Clonally expanded T-cells in the Vss subfamilies could be identified in patients with APL in all but two of the cases studied, predominantly in Vbeta10, Vbeta23, Vbeta3 and Vbeta21. In conclusion, skewed distribution and clonal expansion of TCR Vss subfamily T-cells could be found in patients with APL. The clonal expansion of T-cells were considered to be a specific anti-leukemic immune response by host T-cells activated by the leukemia-associated-antigen.