From a series of 10 patients undergoing surgery with a homograft, two cases are reported in which stenosis of the graft occurred, one in the mitral and the other in the aortic position. The macroscopical appearances of the lesions showed sclerosis and calcification. In the case where histological material was available, there were marked changes in the collagen and elastin, disseminated calcified deposits in the valve, and inflammatory cellular changes over the surface, with a tendency to penetrations into the substance of the valve. One of the factors leading to these graft disorders is the type of chemical treatment which the valve undergoes; a combination of glutaraldehyde solution and oxidation using sodium metaperiodate would appear to be unsuitable in this respect. Emphasis is laid on the very particular clinical features of these two cases (stenosis and valvular incompetence), and on the difficulties in diagnosis of this condition.