A noninvasive method for determining patency of saphenous vein coronary bypass grafts has been developed in our laboratory. The system consists of a pulsed ultrasonic Doppler, a position-sensing arm for the Doppler transducer, a memory oscilloscope, an electrocardiogram, and strip-chart recorder. Patients are studied with the transducer in the suprasternal notch and intercostal spaces. Wherever flow is detected in the anterior mediastinum, a visible dot is stored on the oscilloscope screen at a point corresponding to the location of flow in the mediastinum. By repeated sampling at various depths a composite picture of a proximal section of graft is developed. Peak velocity flow signals from grafts occur during diastole distinguishing them from other arterial flow signals. Twenty-eight patients having 41 patent grafts were studied in a preliminary evaluation of the method. Three examples of angiograms with corresponding ultrasonic arteriograms demonstrate the feasibility and potential value of this new noninvasive technic for assessing patency of saphenous vein coronary bypass grafts.