The growth and migration of endothelial cells are the prerequisites for vascular remodeling. The effects of endothelin (ET)-1 and -3 (ET-1, ET-3) on the proliferation and migration of endothelial cells isolated from bovine adrenal capillaries (BACE) and human umbilical veins (HUVEC) have been investigated. Cell proliferation (measured as DNA synthesis and as total cell number) and migration were significantly increased by ET-1 and ET-3. Dose-dependent proliferation was produced by ET-1 and ET-3 in both cell lines, with maximal effects at 0.1 nM concentration. ET-1 and ET-3 also stimulated BACE and HUVEC mobilization in a dose-dependent manner. The maximal responses were obtained at 10 nM concentration in both BACE and HUVEC. The full agonist for the ETB receptor, ET-(16--21), was able to reproduce the effects of ET on proliferation and migration of both cell lines. Modification of ET-(16--21) at Leu17 and Ile19 and amidation of the COOH-terminal were accompanied by loss of activity. The ETB-receptor antagonist IRL-1038 blocked the migration induced by ET-3 and ET-(16--21), whereas the ETA-receptor antagonist BQ-123 was not effective. We conclude that ETs, by favoring endothelial cell growth and mobilization, can contribute to neovascularization through an autocrine mechanism that requires ETB-receptor activation.