Microvascular repairs of 50 rabbits' femoral arteries averaging 0.9 mm in diameter gave an immediate patency rate of 100 per cent and a follow-up patency rate of 98 per cent after 3-41 days. The patency rate of 50 veins averaging 1.1 mm in diameter was 98 per cent immediately after surgery and 80 per cent after 3-41 days. No anticoagulants or antispasmodics were used. An additional 25 vein repairs with sufficient additional sutures to ensure more accurate apposition of the vein edges resulted in 100 per cent immediate patency and 92 per cent patency when examined during the 2nd week, the period which reveals the truest patency rate. Technical adequacy of the microvascular repair is the most important factor in ensuring final patency.