Analysis of endothelial cell (EC) chemokine receptor expression by RT-PCR revealed that EC essentially do not express CC-chemokine receptors whereas they express all known CXC-chemokine receptors. Endotheliotropic functions of ligands for CXCR-1, CXCR-2, and CXCR-3 have previously been described. We have consequently performed a detailed analysis of endothelial CXCR-4 expression. CXCR-4 is constitutively expressed by quiescent, resting EC. Cytokine stimulation revealed that bFGF upregulates endothelial CXCR-4 expression, whereas TNFα downregulates endothelial CXCR-4 expression. Expression of CXCR-4 mRNA as well as protein is also upregulated in autocrine activated, migrating bovine aortic endothelial cells (BAEC). Furthermore, migrating BAEC preferentially present CXCR-4 on the cell surface as evidenced by cytochemistry and FACS analysis. Lastly, the monospecific CXCR-4 ligand SDF-1 was found to act as a potent inducer of EC chemotaxis. In summary, the data indicate that the CXCR-4/SDF-1 receptor ligand interaction may be an important regulator of activated endothelial cell functions as they occur during vascular remodeling and angiogenesis.