We have investigated the value of cardiopulmonary exercise testing in the pre-operative assessment to patients for abdominal aortic aneurysm repair. Thirty-six patients were entered into the study. All had a pre-operative clinical assessment and investigations including chest radiograph, electrocardiograph, spirometry and echocardiogram with measurement of left ventricular ejection fraction. Each patient performed a symptom limited treadmill exercise test using a STEEP protocol with on-line measurement of respiratory gas exchange. Patients were followed up for 12 months post-operatively by review of casenotes. Thirty out of 36 patients had surgical repair of abdominal aortic aneurysm. There was 1 death in the perioperative period and 2 deaths in the following 12 months. Seven other patients suffered post-operative complications. There were no significant differences in left ventricular ejection fraction, spirometry and peak achieved oxygen consumption (PVO2) between those patients who died or who had post-operative complications and those who had not. However, PVO2 < 20 ml/min/kg was found in 70 per cent of patients who had complications compared with 50 per cent of those who had not. Also 4 patients considered medically unfit for surgery all had PVO2 < 20 ml/min/kg. Cardiopulmonary exercise testing with measurement of PVO2 may be helpful in identifying patients more at risk of post-operative complications but should not be used in isolation without through clinical assessment.