A new technique for mechanical end-to-side anastomoses using the UNILINK anastomotic system is presented. The technique, based on the concept of vessel wall eversion over paired ring pins, is described as is a new device for vessel expansion. To evaluate the technique of end-to-side anastomosis, we detached the left renal artery in 18 rabbits and then reanastomosed them end-to-side to the aorta using the UNILINK anastomotic system. Renal blood flow was evaluated before and after anastomoses with a laser Doppler flowmeter. Animals were separated into three groups of 6 and were killed at 24 hours, 2 weeks, and 16 weeks, respectively. To evaluate the acute effects of vessel expansion, 7 additional rabbits underwent expansion of the aorta without subsequent anastomosis. All vessels were evaluated with light and scanning electron microscopy. A patency rate of 100% was achieved in the 18 animals; histological changes at the anastomotic site were comparable to those described previously for this mechanical anastomotic system. The animal model demonstrates that it is both technically possible and efficacious to perform end-to-side anastomoses of arteries with the UNILINK anastomotic system.