To evaluate noninvasively aortocoronary bypass graft patency, pulsed Doppler echocardiography was performed at the time of postoperative coronary angiography in 120 consecutive patients. Ultrasonic examination of 163 vein grafts was possible. One hundred twenty-seven patent and 14 occluded grafts were correctly identified. Eleven patent grafts could not be recorded, and 11 occluded grafts were falsely diagnosed as patent. The method had an overall sensitivity of 92% and a specificity of 56%. This high sensitivity level may be increased to almost 100% by enhanced technical skill and experience. The low specificity level, although the method must be tested in a larger number of bypass grafts, stresses the importance of correctly identifying other sources of diastolic blood flow. Diastolic flows from the superior vena cava, internal mammary veins, tricuspid valve, mitral valve and right ventricle may be eliminated by careful adjustment of the depth, site and size of the pulsed Doppler electronic sampling gate. Standard echocardiographic landmarks for avoiding confusion with the coronary arteries are also described.