A new technique in preparing a heterograft is presented. Deantigenized calf carotid arteries are obtained by papain digestion and formol tanning. The biochemical determinations show a pronounced reduction in total protein content after papain digestion. The formol tanning gives a good rigidity and elasticity in adapting to different blood volumes without aneurysmal dilatation. Eight dogs were grafted : two died after surgery, two were killed after 35 days and two others 60 days after transplantation, one died after 8 months and one is alive 30 months after transplantation. The good in vivo tolerability has been appreciated. There have been no haemodynamic troubles and no cell changes of rejection. An insignificant quantity of immunoglobulins G has been found in the sera of the animals with heterografts. These data draw attention on the possibility of the use, in clinical practice, of the deantigenized calf arteries.