Visualization of the lumen of the coronary arteries by angiography has greatly expanded the ability of the physician to evaluate the extent of disease in patients suspected of having an ischaemic cardiac disorder. Criteria for coronary angiography have been developed in part by reviewing the experience in the Coronary Artery Surgery Study, CASS. During a five year period at 15 participating sites 24959 consecutive patients undergoing angiography for suspicion of coronary artery disease were enrolled. Chest pain was the dominant symptom in more than 80%. Unstable angina occurred in more than 1/3 of patients classified as definite or probably angina pectoris. The majority of patients were in Canadian Class 2,3. In a study previous reported by CASS a mortality of 002 and a morbidity (myocardial infarction) of 003 was found; presence of left main disease increased mortality 6.8 times. In males, 79% had significant and 12% no CAD; left main disease occurred in 9%. In females 45% had significant and 40% no CAD; left main disease occurred in 4%. The distribution of 1,2 and 3 vessel disease will be presented. From these data and a survey of clinical experience during the past several years, 10 indications for visualization of the coronary artery anatomy by angiography have been developed. These indications are presented for discussion.