Normal human colonic microvascular endothelial cells (HUCMEC) have been isolated from surgical specimens by their adherence to Ulex europeus agglutinin bound to magnetic dynabeads, which bind a-L-fucosyl residues on the endothelial cell membrane. Immunocytochemistry demonstrated the presence of a range of endothelial- specific markers on HUCMEC, including von Willebrand factor, Ulex europeus agglutinin, and PECAM-1. The growing cells form monolayers with the characteristic cobblestone morphology of endothelial cells and eventually form tube-like structures. HUCMEC produce VEGF and express the receptors, KDR and Flt-1, through which VEGF mediates its actions in the endothelium. VEGF induces the tyrosine phosphorylation of KDR and a proliferative response from HUCMEC comparable to that elicited from HUVEC. Upon binding to HUCMEC or HUVEC, ¹²⁵I-VEGF internalizes or dissociates to the medium. Once internalized ¹²⁵I-VEGF is degraded and no evidence of ligand recycling was observed. However, significantly less VEGF is internalized and more is released to the medium from HUCMEC than HUVEC. Angiogenesis results from the proliferation and migration of microvascular and not large vessel endothelial cells. The demonstration that microvascular endothelial cells degrade less and release more VEGF to the medium than large vessel endothelial cells identifies a mechanism permissive of the role of microvascular cells in angiogenesis.