Literature data on angiogenic factors inducing neovascularization of both tumors and normal tissues are reviewed. Properties and structure of the factors isolated from tumors and non-tumoral tissues are considered. Multiple molecular forms of the angiogenic factors are discussed based on the data obtained as well as on analysis of these factors isolation. Acid proteinases appear to be responsible for this multiplicity. Possible fragmentation of the angiogenesis factors by means of proteinases is considered using as an example the factors isolated from brain and hepatoma tissues.