To observe the expression and clonal expansion of TCR Vbeta subfamily T cells induced by AML-M(2a) cells in vivo and in vitro, complementary determining region 3 (CDR3) of TCR beta with variable region genes was amplified by using RT-PCR in both peripheral blood mononuclear cells (PBMNC) and T cells from mixed lymphocyte and tumor culture (MLTC) from four AML-M(2a) patients. The positive products were further analyzed to identify the clonality of T cells by genescan. The results showed that the similarity distribution of TCR Vbeta subfamily T cells was found Vbeta in PBMNC and MLTC. One or two clonality expansions of T cells could be found in predominant TCR Vbeta subfamily T cells induced by A ML-M2a cells from 3 cases in vivo and in vitro. It was concluded that clonal expansion of TCR Vbeta subfamily T cells stimulated selectively by AML-M(2a) cells may be a specific immune response of patient's T cells to AML-M(2a) cells associated antigen. The clonal proliferation of TCR Vbeta subfamily T cells were affected somewhat by environmental difference in vivo and in vitro.