Coronary collaterals were evaluated at arteriography within 1 year of the onset of symptoms of coronary disease in 73 patients with transmural myocardial infarction (TMI), 63 patients with subendocardial myocardial infarction (SMI), and 164 patients with angina pectoris (AP) alone. An occluded artery was present in 79% of patients with TMI, 70% of patients with SMI and elevated serum enzymes, and 42% of patients with AP. Collateral vessels supplied the occluded artery in 91% of patients with AP, 93% of patients with SMI all had postinfarction AP - and 78% of patients with TMI and postinfarction AP, but in only 35% of patients with TMI and no postinfarction AP (p < 0.01). With the treadmill stress test in patients with AP alone and coronary lesions in the anterior wall coronary distribution, 97% had ischemia in leads V4 to V,. Only 25% of patients with coronary lesions in the inferior wall coronary distribution had ischemia in leads III and aVF (positive group) and 75% did not (false negative group). The affected artery was occluded and supplied by collaterals in only 9% of patients of the positive group, but in 57% of the false negative group (p < 0.01). These data and additional findings in the infarction syndromes suggest that in TMI and SMI the presence of collaterals maintains a peri-infarction ischemic zone with subsequent AP. In patients with AP alone, the treadmill stress test is highly predictive of coronary disease in the anterior but not in the inferior wall coronary distribution, in part because of the influence of collaterals.