Differential diagnosis between pericardial disease and other heart conditions has been facilitated by angiography. The hazards of intravenous injections of radio-opaque contrast materials can be avoided by injecting pure carbon dioxide gas. This dissolves rapidly and completely in the blood after serving its purpose. Numerous rapid intravenous injections of 25 to 100 cc. of 100% carbon dioxide have been made in adults without causing subjective discomfort. The apparatus, before the injection, must be flushed thoroughly several times with the gas. The technique of gas angiography described by the authors was used 51 times in 40 patients. With the patient in left lateral position the right atrial border was visualized, which gave positive evidence of disease in 21, normal findings in 18, and equivocal results in 12 cases. In none of the patients studied were there any untoward reactions.