The reproducibility of symptoms, exercise tolerance and haemodynamic variables describing left ventricular pump function have been studied at rest and during repeated supine exercise in ten patients with severe angina pectoris. Two exercise periods were performed about 20 min apart and the breaking point was in all cases determined by angina pectoris. The average working capacity was 22.5 W in both exercise periods. Duration of work, time to onset of angina and pain level at breaking point were not different in the two periods. There were no significant differences at rest nor during exercise for oxygen uptake, arterio-venous oxygen difference, heart rate, cardiac output, stroke volume, left ventricular systolic and end-diastolic pressure, pulmonary artery mean pressure, right atrial mean pressure, stroke work index or left ventricular work. Pressure-time index was significantly (P less than 0.01) higher in the second rest period but systolic pressure heart rate product was not significantly different. The high reproducibility with very small variations of the variables studied should permit the use of this protocol to study the acute haemodynamic effects of pharmacological interventions at rest and during exercise in patients with severe effort-induced angina pectoris.