AbstractCord blood and peripheral‐adult blood were compared as different sources of early endothelial precursor cells (eEPCs). Total mononuclear cells (MNCs) were obtained from both blood types and committed to eEPCs by exposure to fibronectin, VEGF, IGF‐I, and bFGF. Under this condition, MNCs seeded at the density of 3 × 105 cells/cm2 assumed a spindle shape, which was indicative of developing eEPCs, and expanded in a similar manner irrespective to the blood sources. Ulex europaeus agglutinin (UEA‐1) and acetylated low density lipoprotein (acLDL) double staining was present in 90% in both peripheral‐ and cord‐blood eEPCs after 2‐week expansion. Also, the ability of eEPCs to form tubule‐like structures in Matrigel was independent of their blood source, but dependent on the presence of human umbilical vein endothelial cells (HUVECs). eNOS and nNOS were not detectable by Western blotting in both peripheral and cord‐blood eEPCs upon 3 weeks and their mRNA levels were lower than 2% relative to those present in HUVECs. On the contrary, iNOS protein was detectable in peripheral‐blood eEPCs, but not in cord‐blood eEPCs and HUVECs, as well as iNOS mRNA was more concentrated in peripheral‐blood eEPCs than in cord‐blood eEPCs and HUVECs. These data suggest that: (a) peripheral and cord blood can be considered comparable sources of eEPCs when they are expanded and differentiated in a short‐term period; (b) the extremely low expression of constitutive NOS isoforms in the eEPCs of both blood types should markedly reduce their ability to regulate NO‐dependent vasorelaxation; (c) the presence of iNOS in peripheral‐blood eEPCs could improve the process of vasculogenesis. J. Cell. Biochem. 102: 992–1001, 2007. © 2007 Wiley‐Liss, Inc.