The "anoxemia test," together with its clinical applications and limitations, has already been described in detail.1In principle it consists of permitting the patient to breathe a mixture of 10 per cent oxygen and 90 per cent nitrogen for twenty minutes or until cardiac pain appears. Measurements of electrocardiograms taken at intervals during this period reveal in patients with a diminished coronary reserve characteristic changes which are not observed in the presence of an adequate coronary blood flow. The occurrence of pain during the test has not been stressed as a diagnostic feature, because it represents a subjective reaction. In this respect, the present study appears to call for a modification in the point of view. The observations here reported were designed to furnish information concerning the value of a series of tests done over a period of time on the same patients, with particular reference to the diagnosis