Ursolic acid is a triterpenoid with pleiotropic biological effects. In this report, we study the effects of ursolic acid on different key steps of angiogenesis. Our results show that ursolic acid is able to inhibit key steps of angiogenesis in vitro, including endothelial cell proliferation, migration, and differentiation. At the same time, it seems to stimulate other key steps of angiogenesis, such as extracellular matrix degradation by MMP-2 and urokinase. Although ursolic acid can inhibit in vivo angiogenesis in the CAM assay, the different signs of the effects it causes on different steps of angiogenesis force one to be cautious concerning its anti-angiogenic potential. (C) 2004 Elsevier Inc. All rights reserved.