thrombospondin-l may be encoded by a tumor suppressor gene. Dr. O'Reilly discusses angiostatin, an exciting recently discovered factor derived from the fibrinolytic proenzyme plasminogen that inhibits tumor angiogenesis, primary tumor growth, and formation of metastases. In addition to the soluble class of angiogenesis-regulatory factors discussed above, interactions of endothelial cells with components of the extracellular matrix and with other cell types are critical for proper formation of vessels. Drs. Grant and Kleinman discuss the role of laminin and other matrix molecules in regulation...