Tumours recruit neighbouring blood vessels and vascular endothelial cells to support their own blood supply. Recent evidence has indicated, however, that tumours are also capable of mobilizing bone-marrow-derived endothelial precursor cells, inducing them to migrate to the tumour and become incorporated into the developing vasculature. Tumour-derived angiogenic factors promote the recruitment of these cells, which include circulating endothelial progenitor cells and haematopoietic stem and progenitor cells. As clinical trials with anti-angiogenic agents have been confronted with therapeutic hurdles, inhibiting the recruitment of these vascular precursors might provide a novel approach to blocking tumour angiogenesis.