A consecutive series of 93 patients had homograft aortic valve replacement at Green Lane Hospital over a six-month period. Except for 12 assessed at one or two months, the 85 survivors were examined at three months and the clinical degree of aortic incompetence was recorded. Thirty-four of the patients did not proceed to aortography for reasons unrelated to the state of the homograft valve. Fifty-one patients were submitted to cine aortography, using a technique designed to permit a radiological assessment of the degree of aortic incompetence and to reveal details of the anatomy of the homograft valve. Following a brief review of the surgical technique of homograft aortic valve insertion, the radiological anatomy of homograft aortic valves and the mechanism of peripheral aortic incompetence in this situation are described. A radiological method of grading aortic incompetence by cine aortography is presented an the results in the 51 patients are described. The incidence of peripheral space filling and incompetence was considerably lower in the second half of the consecutive series, apparently due to a modification of the surgical technique, namely, the addition of vertical mattress sutures beneath the valve commissures to promote closure of the potential peripheral space. In the whole series of 51 patients, 71% had no significant aortic incompetence. In the latter half of the study after the vertical mattress sutures had been introduced, 84% had no significant incompetence. These results were from operations by a total of six surgeons. A smaller series of patients operated on by one surgeon using vertical mattress sutures was studied by the same methods. Eighteen of 19 patients (95%) had no significant incompetence. Good agreement was found between the radiological and clinical assessment of aortic incompetence, indicating that standard clinical methods can be applied to patients with homograft aortic valve incompetence.