The safety of and the diagnostic information provided by a predischarge exercise test performed 2-7 days after admission to the coronary care unit (CCU) was evaluated in 400 patients less than 65 years of age with suspected unstable coronary artery disease, i.e. probable or definite non-transmural myocardial infarction, progressive angina pectoris or recurring chest pain of recent onset ('new chest pain'). No serious complications occurred. Signs of ischaemia during exercise tests were more common in older than in younger men and more often found in subjects with than without pathological findings in resting ECGs in the CCU. Above 45 years of age, more than half of the men with progressive angina or non-transmural MI had SI depression greater than or equal to 2 mm and/or limiting chest pain, whereas men less than 45 years of age had a 10-25% incidence of corresponding findings in the test. In women above 55 years with progressive angina or non-transmural MI, 30-35% had ST depression and/or limiting chest pain at the test while 20-30% of women below 55 years of age had similar findings at the test. Beta-adrenoceptor blockade was used by half of the patients but did not seem to conceal signs of severe ischaemia. Thus a predischarge exercise test can be performed safely in patients with suspected unstable coronary artery disease in order to support or reduce the suspicion of severe disease.