OBJECTIVE To investigate the correlation between the sensitivity to the tumor necrosis factor- related apoptosis inducing ligand (TRAIL) and the level of expression of the death receptor 5 (DR5) on the surface of tumor cells.METHODS Anti-DR5 mAbs were used to directly detect the level of expression of DR5 on the surface of tumor cells. Using a TRAIL apoptosis kit and flow cytometry, the sensitivity of the tumor cells to TRAIL-induced apoptosis was determined and the correlation between DR5 expression and sensitivity to TRAIL analyzed.RESULTS The expression level of DR5 on the surface of different tumor cells was as follows: 97.9% in U937 cells, 95.1% in Jurkat cells, 93.8% in SW480 cells, 86.2% in HCT116 cells, 64.2% in HL-60 cells, 46.6% in Hela cells and 13.1% in K562 cells. The TRAIL-induced apoptotic rate was 72.6% in U937 cells, 85.2% in Jurkat cells, 78.6% in SW480 cells, 70.2% in HCT116 cells,60.1% in HL-60 cells, 45.4% in Hela cells and 12.3% in K562 cells. Statistical analysis showed there was a significant positive correlation (r=0.997, P<0.001) between DR5 expression and sensitivity to TRAIL.CONCLUSION The sensitivity of tumor cells to TRAIL is related to the level of expression of DR5 on the surface of tumor cells. These results confirm the importance of DR5 expression for induction of apoptosis by TRAIL.