Results of animal experiments are presented on the applicability in the low pressure system of a collagen prosthesis, which has been used successfully, for considerable time, in the arterial replacement in patients and dogs. Grafts of up to 7 cm in length were implanted into the suprarenal segment of the inferior vena cava (v. cava caudalis) in dogs and observed clinically over a period of more than 500 days. Histological investigations were made. With some limitations the results obtained are considered as good and point towards the applicability of the examined graft material in the low pressure system.