The diagnostic and prognostic value of ambulatory ST recordings after admission to the CCU and before discharge was compared to a symptom-limited predischarge exercise test in 170 men with unstable angina pectoris or non-Q wave myocardial infarction. ST depression in recordings before discharge identified a small group of patients (18%) out of whom 23% had a myocardial infarction within 3 months compared to 7% in those without this finding. The exercise test gave more diagnostic information, with ST depression found in 52% including 70% of those with ST depression at Holter monitoring. After 3 months, 13% of patients with ST depression at exercise test had a myocardial infarction compared to 5% in the other patients. ST depression at exercise also indicated an increased risk of myocardial and future severe angina over a longer time period. Thus ST recordings are recommended before discharge in all patients after an episode of unstable coronary artery disease as it identifies the patients with the most severe prognosis who might benefit from early revascularization. In those without ST depression at Holter a predischarge exercise test will give further information regarding the long-term risk for angina and coronary events.