The authors report an anatomical study of the ductus venosus in the stillborn fetus based on resin-corrosion casts and angiography. Study in adult material was done by dissection. In the first part of this paper the classical anatomy of the ductus venosus is described and an anomalous case of a hepatic parenchymal bridge between the left and caudate lobes of the liver is reported. In the second part of this paper study of patency and dilation of the ligamentum venosum to a diameter exceeding 10 mm in adult cadavers is presented. A brief study of portal flow demonstrated that an increase in flow of 30% can be obtained by experimental induction of patency. A patent ligamentum venosum was grafted onto the abdominal aorta in the rabbit. The transplanted segment was fully patent and competent immediately after grafting, but showed thrombosis when the animal was sacrified two months after the operation. In the opinion of the authors, it may be possible to use the patent ductus venosus in man once the problems of long term resistance and patency have been solved. The latter problems are currently under investigation in our laboratory.