Venous allografts were evaluated in two models. Lyophilized allograft veins used as interposition grafts in the infrarenal aorta of the canine were studied and found to be patent at 1 year. Pathologic examination of the grafts revealed mild intimal hyperplasia and persistence of the basic structure of the lyophilized vessel. The ability of venous tissue to elicit an antibody response when transplanted into an allogeneic recipient was studied in the rat using the lymphocyte cytotoxicity assay. Fresh and Me2SO-cryoprotected frozen veins produced circulating antibody when used as interposition grafts in the infrarenal aorta of the rat. Lyophilized and noncryoprotected frozen veins did not induce measurable antibody. Lyophilized allograft veins are a nonimmunogenic vascular graft material with acceptable long-term patency.