Objective:To investigate whether VLA-5 and VLA-6 are involved in facilitating en-dothelium-oriented transmigration of hematopoietic stem/progenitor cells. Methods:Purified hu-man CD34+ cells were subject to ex vivo transmigration assay and blocking experiments throughtranswell filter inserts coated with human umbilical vein endothelial cells (HUVECs). Four-colorfluorescence-activated cell sorting (FACS) analysis was applied to detect the expression profilesof adhesion molecules and chemokine receptor CXCR-4 on CD34bright cells. Results:Stromal cell-derived factor (SDF)-1-induced transmigrations of both mobilized peripheral blood (mPB)-(56.6±20. 1)% and bone marrow (BM)- (15. 6±1. 8)% derived CD34+ cells were significantlyfacilitated through HUVECs-coated transwell filter insters compared with noncoated ones, whichwere efficiently blocked by preincubation of CD34+ cells with neutralizing antibodies to VLA-5,or VLA-6, or both of them; meanwhile the proportions of migrating CD34+ cells through bothHUVECs-coated and noncoated transwell filter inserts in BM were significantly lower than thosein mPB; the different percentages of migrating CD34+ cells between in mPB and BM were corre-lated with their variable expressions of VLA-5 and VLA-6, but not for VLA-4 or chemokine re-ceptor CXCR-4. Conclusion:Facilitating HS/PCs transmigrations through HUVECs are involvedin both VLA-5 and VLA-6.