To investigate the value of apoptosis of the allo antigen specific T cells induced by Fas/FasL pathway in preventing graft versus host disease (GVHD), the CD34 + cells transfected with FasL or not, used as stimulus cells, were mixed with allo antigen specific T lymphocytes in presence or absence of IFN γand IL 2. After 5 days, apoptosis of T cells was detected by TdT nick end mediated dUTP labeling (TUNEL) and flow cytometry (FCM). The affects of these two cytokines on CD34 + cells in the graft were also compared. The ratio of apoptosis of T cells was 12.1±1.5 % when CD34 + cells transfected with FasL was used as stimulus cells, much higher than that of CD34 + cells non transfected (3.2 ±1.1 %, P <0.01). And in presence of IFN γ or IL 2, the ratio reached 20.1±2.3 %, 17.6±1.3 % respectively ( P <0.01). However, IFN γ up regulated Fas expression of CD34 + cells and increased the sensibility of CD34 + cells to soluble FasL(sFasL); IL 2 showed no such affect. It is possible to induce apoptosis of the allo antigen specific T cells of grafts activated by allo antigen by exogenous Fas ligand expressed on recipient cells and this might provide a new approach for preventing GVHD and IL 2 may be more suitable for clinical application. To investigate the value of apoptosis of the allo antigen specific T cells induced by Fas / FasL pathway in preventing graft versus host disease (GVHD), the CD34 + cells transfected with FasL or not, used as stimulus cells, were mixed with allo antigen specific T lymphocytes in presence or absence of IFNγand IL 2. After 5 days, apoptosis of T cells was detected by TdT nick end mediated dUTP labeling (TUNEL) and flow cytometry (FCM). The affects of these two cytokines on CD34 + cells in the ratio of apoptosis of T cells was 12.1 ± 1.5% when CD34 + cells were transfected with FasL was used as stimulus cells, much higher than that of CD34 + cells non transfected (3.2 ± 1.1%, P <0.01 ), And in presence of IFN γ or IL 2, the ratio reached 20.1 ± 2.3%, 17.6 ± 1.3% respectively (P <0.01). However, IFN γ up regulated Fas expression of CD34 + cells and increased the sensibility of CD34 + cells to soluble FasL (sFasL); IL 2 showed no such affec It is possible to induce apoptosis of the allo antigen specific T cells of grafts activated by allo antigen by exogenous Fas ligand expressed on recipient cells and this might provide a new approach for preventing GVHD and IL 2 may be more suitable for clinical applications.