Anastomoses between the bronchial and pulmonary arteries were studied by means of neoprene casts and by injection of a radiopaque substance or dyes. In fcetal lambs and newborn kittens and puppies there were numerous precapillary connections between the two arterial systems, the bronchial arteries appearing as branches of the pulmonary artery. In lambs a few weeks old and in adult cats there were coiled constricted connections between the two arteries. In two adult dogs no precapillary anastomoses were found, but in an 8 weeks old puppy there were constricted anastomoses. No evidence was found suggesting that a great deal of blood flows through these connections in life, but they are probably the basis of some of the shunts which develop in disease. It is suggested that there may be frequent communication between the two arterial systems in fcetal life while the pressure is the same in both, but that after birth the connections close down to different degrees in different species.