The study investigates the effects of vascular permeability factor (VPF), a protein purified from guinea pig line 10 tumor cells, on endothelial cells and angiogenesis. VPF was found to stimulate the growth of vascular endothelial cells in vitro and promote angiogenesis in vivo, particularly in healing rabbit bone grafts and rat corneas. The growth-promoting activity of VPF was confirmed through multiple lines of evidence, including SDS-PAGE analysis, immunoadsorption, and binding studies. VPF was shown to bind specifically to endothelial cells and form high-affinity complexes with a putative VPF receptor. Unlike other growth factors, VPF did not stimulate [³H]thymidine incorporation or promote the growth of other cell types. The unique properties of VPF suggest that it may play a specific role in increasing vascular permeability, endothelial cell growth, and angiogenesis.The study investigates the effects of vascular permeability factor (VPF), a protein purified from guinea pig line 10 tumor cells, on endothelial cells and angiogenesis. VPF was found to stimulate the growth of vascular endothelial cells in vitro and promote angiogenesis in vivo, particularly in healing rabbit bone grafts and rat corneas. The growth-promoting activity of VPF was confirmed through multiple lines of evidence, including SDS-PAGE analysis, immunoadsorption, and binding studies. VPF was shown to bind specifically to endothelial cells and form high-affinity complexes with a putative VPF receptor. Unlike other growth factors, VPF did not stimulate [³H]thymidine incorporation or promote the growth of other cell types. The unique properties of VPF suggest that it may play a specific role in increasing vascular permeability, endothelial cell growth, and angiogenesis.