The identification of progenitor cells in adult peripheral blood has significant clinical implications for the treatment of multiple diseases including the biggest killers in the world, cancer and cardiovascular disease. Moreover, particular emphasis has been placed on the research into vascular progenitor cells with pro-angiogenic potential. We recently described and characterised a human umbilical cord blood (UCB) derived CD133+ population of non-adherent endothelial progenitor cells (naEPCs) which generated perfused vasculature in vivo. Using these cells we sought to identify novel biomarkers which would contribute to the isolation of naEPCs as well as vascular function. Gene expression analysis of naEPCs compared to donor matched human umbilical vein endothelial cells (HUVEC) revealed that a cell surface adhesion molecule, de-identified here as Bm1, was significantly upregulated in the naEPC population. Furthermore, flow cytometric analysis confirmed surface expression of Bm1 on naEPCs versus its absence on HUVEC. Further characterisation of Bm1 expression on other circulating blood lineages revealed that it was not expressed by CD4+ T cells, CD14+ monocytes, CD16+ natural killer cells and CD19+ B cells. Functionally, Bm1+ naEPCs are pro-angiogenic as demonstrated by increased tube formation when co-cultured with HUVEC in the Matrigel 3-dimensional matrix in vitro. The generation of a Bm1-/-mouse has further addressed a role for Bm1 in in vivo neovascularisation. Briefly, a number of vascular deficiencies have been identified with (i) Bm1-/- mice exhibiting impaired in vitro vascularsprouting in an aortic ring assay and (ii) a reduction in vessel formation within Matrigel plugs in vivo. Taken together, this study has identified Bm1 as a new biomarker for naEPCs and implicated this adhesion molecule in the regulation of vascular function both in vivo and in vitro. Future studies will reveal whether it can be manipulated to combat pathological vasculogenesis.