End-to-end and end-to-side anastomosis was performed on 1--4 mm diameter arteries and veins of dogs using 9--0 suture and microvascular technique. After peraortic in-vivo glutaraldehyde perfusion fixation was performed, specimens were immersed in fixative and later removed for SEM examination of intraluminal surfaces. Platelet and leucocyte aggregation was seen at 24 hours at sites of endothelial disruption. Consecutive stages of neoendothelialization were seen at intervals up to 6 months. Abnormal intimal surfaces are described at sites of high flow or jet stream turbulence in arteriovenous shunts or end-to-side arterial anastomosis. If stenosis of the lumen does not occur, intimal healing and 100% patency rates can be expected.