Techniques to reinforce a vessel wall without occluding its lumen are being studied. In pilot experiments the intimal surface along a short segment of vein was coated with plastic by injecting liquid silicone rubber into a vessel, spreading the material along the vessel with a balloon catheter, allowing polymerization and then removing the catheter. In 17 experiments in the iliac vein of rabbits, successful coating was obtained in 5. If perfected, these techniques might be applicable to treating some aneurysms or arteriosclerotic plaques.