Four patients with heart valve prostheses developed Candidate endocarditis. At autopsy the foci of infection were confined to patches of neoendocardium that appeared to have developed as ingrowths of host endocardium onto the sewing cloth of the artificial valve. This suggested that one mechanism of fungal infection is related to the presence of the neoendocardium rather than to the cloth or metallic substances of the valve itself. Future studies might be directed toward inhibiting the development of the neoendocardium or to agents preventing its susceptibility to infection.