Adult bone marrow and peripheral blood contain small subsets of mononuclear cells that can be differentiated into endothelial-like cells in vitro. Experimental and clinical transplantation of such cell isolates--often referred to as endothelial stem/progenitor cells--into ischaemic or infarcted areas shows their incorporation into sites of new vessel growth along with improvement of regional blood flow. Emerging evidence suggests that these beneficial effects on vascular growth can be attributed to the paracrine activation of resident endothelial cells, rather than their integration into new endothelium. Autologous endothelial progenitor cells can also substitute for native vessel-derived endothelial cells in tissue-engineered vascular autografts.