Placing the omentum on the brain surface by surgical transposition or transplantation will result in the development of numerous neovascular connections between these two structures. This phenomenon occurs even in the absence of cerebral ischemia, which raised the question as to whether an angiogenic factor was causing the response. A lipid material obtained from the omentum contains a potent angiogenic factor extractable in a chloroform-methanol solvent mixture. Angiogenesis created by this material was observed in the rabbit cornea after only a single injection of the substance. The angiogenic material obtained from the omentum is abundant in supply. This important characteristic offers promise for the purification and identification of its structure, which should allow for extensive animal and clinical studies dealing with the development or inhibition of angiogenesis.