Tumor angiogenesis is one of the most important fields of cancer research. It is important to identify the putative targets for antiangiogenic strategies. To date, a number of angiogenic agents have been identified: bFGF, the different VEGF isoforms, integrins, proteases (matrix metalloproteases and serine proteases),... Furthermore, several physiological anti-angiogenic agents have been isolated such as endostatin, angiostatin, 16 K prolactin,.... The recent development of mice deficient for one gene involved during angiogenesis gives a new insight into the molecular mechanisms regulating this process. It leads to the identification of plasminogen activator inhibitor-1 or PAI-1 as a new target for tumor treatment. Although, PAI-1 is very attractive as a target for new therapeutic strategies, a better understanding of its mechanism of action is needed urgently.