The issue of the potential risks of treatment with angiogenic growth factors is an important one. Does therapeutic angiogenesis promote the growth of dormant tumors or atherosclerotic plaques? Is it possible to obtain a functional vasculature with vascular endothelial growth factor (VEGF) or fibroblast growth factors (FGFs) without causing hypotension, edema, or vessel malformation? The therapeutic window for angiogenic growth factors is not well defined. To some extent, this is due to failure of animal models to mimic human disease and differences in genetic susceptibility. Although there is no doubt that a collateral circulation can be developed using appropriate growth factor(s), genuine risks are involved, and at the present time, it is only once the growth factors have left the laboratory that we start getting an idea of what the associated risks may be...