This study compared the histological patency rates of anastomoses of the femoral artery. Twelve rabbits weighing about 2 kg were studied. Both the right and left femoral arteries were cut. The control group had no damage to the vessel, saline irrigation, and micro-anastomosis. Experimental group I had a crush injury to the vessel, saline irrigation, and micro-anastomosis. Experimental group II had a crush injury, saline irrigation, 100 U/ml heparin irrigation, and micro-anastomosis. Experimental group III had the same treatment as experimental group II plus the systemic application of 100 U/kg heparin iv. The histological patency rates were compared. The patency rates of the control group 30 min and 3 days after the anastomosis were 100 and 83%, respectively. The respective rates for experimental groups I and II 30 min and 3 days after the anastomosis were 100% in all cases. The respective rates in experimental group III were 100 and 83%. In this study, no significant correlation was observed between the patency rate and the effects of local irrigation or the systemic application of heparin on the microvascular anastomosis of the rabbit femoral artery. However, the patency rate tended to decrease concomitantly with an increase in surgery time. Increased bleeding was observed after the systemic application of heparin. Obvious damage to the crush-injured vascular endothelium was detected on histologic examination of the micro-anastomosed area. In addition, some vessels subjected to crush injury contained thrombi attached to the vascular endothelium. No preventive effect of heparin on thrombus formation was observed.