Soto tumor growth in animals and in man is accompanied by neovascularization. New capillary growth is elicited by a dif-. fusible factor generated by malignant tu-mor cells. In the absence of neovasculariza-tion most tumors might become dormant at a tiny diameter, perhaps 2–3 mm.*** Although evidence for these statements is still indirect and fragmentary, it seems appropriate to speculate that the inhibition of angiogenesis, ie, anti-angiogenesis, may provide a form of cancer therapy worthy of serious exploration. The evidence for such a contention, based on recent findings in our own laboratory and others, will be exanined in this report.