CD134, a member of the tumor necrosis factor receptor superfamily, plays a crucial role in T cell survival. In this study, peripheral blood mononuclear cells (PBMCs) stimulated with phytohemagglutinin (PHA, 50 microg/ml) were treated by CD134 mAb (1 microg/ml, 5 microg/ml, 10 microg/ml) for 6 h, 12 h, 24 h and 48 h. The level of perforin mRNA was measured by reverse transcription-polymerase chain reaction (RT-PCR) technique. Our data showed that the expression of perforin mRNA in PBMCs was down-regulated by CD134 mAb in a dose-dependent manner in range of 1 microg/ml to 5 microg/ml and dropped down to its minimum on 24 h (p<0.05). The level of perforin mRNA reached a plateau when the concentration of CD134 mAb exceeded 5 microg/ml. In conclusion, CD134 mAb can inhibit perforin expression, which may enhance the ability of T cells for survival.