Calcification is a major cause of glutaraldehyde-fixed bioprosthetic valve failure. Recent studies have shown that dystrophic calcification shares basic features with normal bone mineralization, including crystal initiation through the mediation of cell membranes, usually in the form of extracellular vesicles. In this study, we observed that calcification of the myocardium of DBA/2J mice was inhibited or reversed by diets supplemented with 100 mg/kg diet diphenylhydantoin (dilantin) for 70 days, with a calcification incidence of 25% in the dilantin group versus 58% in control. We further studied the effects of dilantin on bioprosthetic valve calcification. Three groups of young male Sprague-Dawley rats (100 g, 9/group) were implanted subcutaneously with 1-cm2 pieces of glutaraldehyde-fixed bovine pericardium. Controls were fed a ground chow for 45 or 90 days postimplantation; experimentals received the same chow for the first 45 days postimplantation and then were fed the same diet supplemented with 1000 mg dilantin/kg for the succeeding 45 days. Calcium content (μg/mg dry weight) of the implants in the dilantin group was 137 ± 18.6 versus 214 ± 34.3 in 90 days control and 79.9 ± 41.5 in 45 days control (means ± SD, P < 0.01 and P < 0.05 respectively, t test). The tibia calcium content of the dilantin group was not significantly different from 90 days control. We conclude that orally administered dilantin inhibits calcification of glutaraldehyde-fixed bovine pericardial implants preferentially. It does not cause decalcification either of implants that have already calcified or of the bones. The anti-calcification effect of dilantin may be associated with its anti-vitamin D effect.