The purpose of this study was to delineate the clinical, ECG, and angiographic features of a large series of consecutive patients with angina at rest. Transient ST segment elevation during pain was observed in 219 patients (group I), while 220 patients showed ST segment depression during pain (group II). Group II patients were found to have higher incidence of hypertension (p less than 0.001), prior myocardial infarction (p less than 0.0005), history of exertional angina (p less than 0.0005), and a progressive aggravation of symptoms before hospitalization (p less than 0.0005), while group I patients had a prevalence of recent onset angina (p less than 0.05) and more frequently developed severe ventricular arrhythmias during pain (p less than 0.0005). Furthermore, a larger number of patients showing ST segment depression during chest pain had multivessel disease (p less than 0.0005), left main involvement (p less than 0.005), and lower values of left ventricular ejection fraction (p less than 0.001) than patients with ST segment elevation during pain. Survival curves of medically treated patients showed a significantly better long-term prognosis in patients of group I (p less than 0.01). The direction of the ST segment shift during anginal attacks at rest may therefore allow a classification of patients included into the broad spectrum of unstable angina. This distinction should be taken into consideration in studies aimed at evaluating long-term prognosis or the results of medical and surgical therapy.