Myocardial imaging with 133Xe and a gamma camera was employed to evaluate total and regional myocardial blood flow. The technique detected vasodilatation after injection of papaverine or diatrizoate. Contrast medium caused transient vasodilatation with return to baseline flow within 5 min. Myocardial tissue flow tended to decrease as coronary artery stenosis became more severe. There was overlap of flow measurements in patients with and without coronary artery disease. Coronary flow measurements made at rest are not considered to be an essential clinical tool. Greater diagnostic benefit is obtained from the scintigram which distinguishes between akinesia caused by ischemia and akinesia due to extensive scarring.