Conventional radiographs of lungs of calves which had been injected post mortem with barium sulphate could not be used to demonstrate vessels smaller than 50 μ in diameter. To overcome this difficulty, frozen sections 50–150 μ thick were floated on to high resolution photographic plates and contact microradiographs made using soft radiation. The resultant microradiogram was then viewed and photographed with the light microscope. It was possible to visualize the smaller arterioles and the capillary networks around the alveoli. The technique is simple and gives reproducible results.