A method to accelerate the endothelialization of vascular prostheses by seeding venous tissue fragments was developed. A piece of peripheral vein was obtained, chopped into small fragments, and stirred into 20 ml of saline, making a tissue suspension. This suspension was sieved through the wall of a highly porous vascular prosthesis (water porosity: 3,600-4,000). The prostheses, (7 mm ID and 5.7 cm in length) seeded with tissue fragments, were implanted into the thoracic descending aortae of 20 dogs, and were removed from 1 to 371 days after implantation. Ten prostheses, preclotted with fresh blood, were used as controls. In the seeded grafts, an infinite number of endothelial cells migrated and proliferated from the fragments. These had produced numerous capillaries by 5 days after implantation that had reached and opened onto the luminal surface of the prosthesis. From these openings, numerous endothelial cells spread out and formed colonies. With the increase in the size of the colonies, the inner surface was completely endothelialized within 5 weeks. This quick neointimal formation by seeding venous tissue fragments might be applicable to several artificial organs.