The study was to understand the impact on the proliferation and cytotoxicity of donor's T cells during mobilization with rhG-CSF. The peripheral blood mononuclear cells (PBMNC) were collected from 15 donors before mobilization and on fifth day of mobilization with rhG-CSF. After the PBMNC were activated with 500 ng/ml of CD3 monoclonal antibody and 500 microg/ml of rhIL-2 for 96 hours, the activated T cells were collected for testing proliferation, cytotoxicity, Fas expression, perforin and Fas ligand (FasL) mRNA expression, the IFN-gamma concentration in the culture medium of the activated T cells was determined by radioimmunoassay. The results showed that the proliferation activity of T lymphocytes and the cytotoxicity of T cells activated with CD3 monoclonal antibody and rhIL-2 were reduced markedly after mobilization with rhG-CSF (P < 0.05). The Fas molecule expression in the activated T cells was very high both before and after mobilization with rhG-CSF (P > 0.10). The activated T cells expressed perforin mRNA and didn't express FasL mRNA both before and after mobilization with rhG-CSF. The concentration of IFN-gamma in the culture medium of the activated T cells decreased significantly after mobilization with rhG-CSF (P < 0.01). It is concluded that activity of proliferation and cytotoxicity of donor's T cells is impaired after mobilization with rhG-CSF.