Forty-nine patients deemed to have a low in-hospital risk after 24 hours observation for suspected myocardial infarction, underwent exercise testing 24-48 hours after admission. Thirty-six patients had adequate exercise tolerance and follow-up of this group at one year, showed that no major cardiac event occurred. Of the 13 patients whose performance was inadequate, five were found to have critical lesions at angiography. Early exercise testing is a useful prognostic test, permitting confident early discharge of patients who do not have threatening coronary disease. If this approach was adopted throughout the country, the number of patients, referred for angiographic assessment prior to loss of myocardium could be substantially, and justifiable increased.