A characteristic and transient early diastolic precordial murmur is commonly heard in patients with renal failure. On the basis of its clinical characteristics, this murmur has previously been attributed to functional aortic incompetence. We undertook a formal cardiac investigation, including aortography, in six of eight patients with renal failure in whom such a bruit developed. Aortic regurgitation was detected in only one of the six. Echocardiography revealed no abnormality of aortic-valve function but did indicate the presence of a small pericardial effusion in each of the five patients examined. We conclude that the early diastolic murmur associated with renal failure does not usually arise from functional aortic incompetence but may be a sound of pericardial origin.