This investigation characterized venous endothelial healing after surgical manipulation. Procedures were performed on jugular and femoral veins in 21 mongrel dogs without systemic anticoagulation. Veins were harvested at varying intervals and vessel structure evaluated with light, transmission, and scanning electron microscopy. Veins that were mobilized or stripped of adventitia demonstrated 25% to 50% endothelial loss at one hour. Endothelial damage was rapidly repaired with complete healing observed in some veins at 48 hours. Tourniquets and clamps resulted in prominent medial and endothelial injury at occlusion sites. Eighteen of 24 transected veins remained patent for the study period. Endothelial healing was unaffected by tension at anastomoses. These observations confirm that venous endothelium receives nutrition by luminal diffusion. The healing process of venous anastomoses is characterized by an early fibrin sleeve sealing the anastomotic site; endothelial bridging of defects can be noticeably delayed by excessive fibrin deposition.