Coronary artery lesions were compared in 71 patients with unstable angina, 15 patients with non-Q wave myocardial infarction (MI), and 40 patients with stable angina. In the unstable angina group, 29 patients had new-onset angina, 31 had crescendo angina, and 11 had rest angina. In a subgroup of patients with unstable angina, three-vessel disease was less frequently (P < 0.05) seen in patients with new-onset angina (10.3%) than in the patients with crescendo angina (51.6%) or rest angina (54.5%). An angina-producing artery could be identified in 59 patients with unstable angina, in 11 with non-Q wave MI, and in 30 with stable angina. Type II eccentric stenosis (asymmetric narrowing with narrow neck and overhanging irregular edges) was present in 31 patients (52.5%; P < 0.01) with unstable angina, in 7 (63.6%; P < 0.01) with non-Q wave MI, and in only 2 (6.7%) with stable angina. Abrupt occlusion of a vessel was observed in 7 patients (11.9%) with unstable angina and in 2 (18.2%) with non-Q wave MI. None of the patients with stable angina had this type of occlusion. In the group of unstable angina and non-Q wave MI, angiographic evidence of intracoronary thrombi was present in 16 (27.1%) and 3 patients (27.3%), respectively, but in stable angina in only 1 patient (3.3%; P < 0.05). Intracoronary thrombi were most frequently found in rest angina (88%; P < 0.001) and crescendo angina (33.3%; P < 0.01) compared with new-onset angina (3.7%).(ABSTRACT TRUNCATED AT 250 WORDS)