PreviewHow does a major medical center in which conventional and HMO types of payment systems have functioned side by side for more than ten years approach the use of major, expensive procedures such as arteriography and coronary artery bypass surgery? Dr Peterson explains how the indications for these two procedures have evolved at Park Nicollet Medical Center since 1970, compares the center's results with those of the Coronary Artery Surgery Study, and relates the positive impact the “HMO perspective” has had on care of all patients with coronary artery disease.