One of the best methods of delineating the bronchial tree, especially in children, without resorting to surgical operation is bronchography. Today this is performed by anesthetizing the larynx, trachea, and major bronchi, introducing a tube into the trachea, and injecting a liquid radiopaque contrast medium into the bronchial tree. When, however, one considers the multitude of bronchial and pulmonary diseases, it appears that this technic (tracheal intubation, tracheal liquid instillation) is infrequently used as a primary diagnostic procedure, due presumably to the discomfort and complications experienced by the patient during and after its performance (1). The authors are in the process of developing an air inhalation technic for demonstrating the bronchial tree without the use of liquid contrast medium and with minimal or possibly no anesthesia. The specific objectives of the experimental studies to be reported here were as follows: 1. To determine whether dry aerosol powders, gases of rare earths of high atomic number, or mixtures of gases with vapors of radiocontrast material may be used for radiographic demonstration of the bronchial tree and lung parenchyma. 2. To determine the photographic effect of the radiopaque dry, liquid, aerosol, and gas mixtures at different wave lengths of irradiation (including both gamma and neutron beams). Method and Results We have used dry micronized barium sulfate for visualization of the bronchial tree in dogs. Barium sulfate particles measuring 0.1 to 50 microns can be introduced into the bronchial tree and produce a bronchogram. In our first group of ,3 dogs, 15 separate bronchograms were obtained. The animals were anesthetized with intravenous Nembutal and then intubated. A Bird positive-pressure breathing apparatus was used for controlled respirations. Dry barium aerosols were produced by mechanical agitation in a Waring type blender, the size and amount of the particles being controlled by the speed of the agitation process and the quantity of oxygen through the system. Approximately 30 gm. of different micronized mixtures of barium sulfate were put into the blender to prime it. Several 3/4 × 3/4-inch gum rubber tubes were also added to the mixture to increase the agitation process. The Bird apparatus was connected to an inlet opening into the blender, and an outlet opening was connected to the intubation tube within the dog. After 250 deep inspiratory breaths controlled by the Bird positive-pressure apparatus (involving approximately 20 cm. of water pressure, 20 inspiratory breaths per minute) an inhalation type of bronchogram was obtained. During the inhalation the blender was operating at medium speed. In a second group of 4 dogs, the bronchial mucosa was prepared with 0.25 gm. of Methocel,2 and 15 separate bronchograms were obtained.