Emergency coronary angiography was performed in 188 patients with treatment-resistant unstable angina. Criteria analysed were: duration of angina less than 72 h; angina despite heparin and nitroglycerin infusion; no significant S-T segment elevation in the ECG; creatine-kinase rise up to 150 U/l. Coronary heart disease (CHD) was found in 130 patients (group A). In 47 of them a recent coronary occlusion was demonstrated angiographically (main stem: 1; anterior interventricular branch: 8; circumflex branch: 27; right coronary artery: 11 patients). An at least 90% occlusion of one coronary artery was found in 58 patients. A 75% stenosis of several vessels was found in 25 patients making it impossible to identify the vessel that had caused the angina. A bypass operation was performed in 62 patients within two weeks. During the acute coronary angiography, intracoronary streptokinase infusion was performed in 11 (success rate 55%), percutaneous transluminal coronary angioplasty in 26 (success rate 88%). In 58 patients (group B) CHD was excluded. The final diagnosis in these was: mitral valve prolapse (31); pericarditis (6), dilated cardiomyopathy (3); coronary anomaly (3); muscle bridge in the anterior interventricular branch (2): normal (13). CONCLUSIONS It is not possible to decide with certainty, in the absence of typical infarction signs in the ECG and clinically, whether treatment-resistant angina is due to CHD or other causes. Acute coronary angiography is indicated in such cases, because even without S-T segment elevation an acute coronary occlusion is present in 25%, and in 50% of cases an acute therapeutic intervention is indicated.