The present invention provides a method of inhibiting angiogenesis within a tissue by providing exogenous PEDF to cells associated with the tissue. The presence of exogenous PEDF inhibits angiogenesis within the tissue, in part by interfering with the ability of vascular endothelia to expand within the tissue. The invention also provides a method for determining the severity of a tumor be assaying for the presence of PEDF within the tumor. To facilitate the inventive methods, the present invention provides pharmaceutical compositions including sources of PEDF.