1. Cinefluorography: One of the image amplifiers we have employed (Philips) is equipped commercially with an f 1.5 50-mm. lens mounted at its focal length from the output phosphor; the emergent rays are thus approximately parallel. The camera lens, focysed at infinity, is brought into apposition to that of the image amplifier; this optical arrangement is not at all critical. An f 1.4 25-mm. camera lens reduces the 12- to 15-mm. phosphor image so that a complete circle is visible on each frame of 16-mm. motion-picture film. With an f 1.6 50-mm. lens the complete 16-mm. frame is covered, but a small portion of the top and bottom of the circular amplifier phosphor image is cut off. Comparable results have been obtained with a Westinghouse image amplifier made available for experimental purposes. Fluoroscopic viewing is accomplished either directly through the amplifier lens or by a right-angle telescope. A closed circuit television pick-up can be substituted for the motion-picture camera. We have found it entirely feasible to process relatively short runs of 16-mm. film such as are obtained in ten or fifteen seconds as, for example, in angiocardiography. We have used standard x-ray solutions right in the x-ray dark room. It has thus been possible to view by projection angiocardiographic films in clinical cases within one hour after the study is performed. The detail of projected single frames is not nearly so good as that of a direct conventional roentgenogram but the information desired from such a study concerns dynamic processes and much can be gained from viewing the films as motion pictures. It is impossible to glean such data from one or even a series of still radiographs. In addition, a certain stereoscopic effect is simulated by the respiratory and rotatory motion of the patient, which should not be completely discouraged during cinefluorographic work since additional information is provided by the slight differences in projection which result. To date we have used cinefluorography particularly in studies of the heart, including angiocardiography (1–4). In small animals and in infants it has been possible to use x-ray intensities below the usual fluoroscopic levels and yet obtain satisfactory motion picture film exposure at speeds up to 64 frames per second. Experimental studies have been done at speeds up to 300 frames per second and slight increases in the x-ray intensity would certainly make such ultra-slow motion analysis quite feasible. A good film at 64 frames per second showing lung detail in a 28-cm. chest was recently obtained with a new Philips tube; the roentgen beam intensity at the patient entrance portal was 6.8 r per minute, and at the surface of the amplifier 0.084 r per minute (60 kv, 1 ma, 30 in. target to image amplifier).