Calcification is a major problem in glutaraldehyde-preserved bioprosthetic valves. We have used bovine pericardium processed in a solution containing 0.625% glutaraldehyde, 0.05M HEPES buffer and 0.26% magnesium chloride in saline. And, we also treated the glutaraldehyde-preserved bovine pericardium with a surfactant, Triton X - 100 to reduce calcification. To evaluate the degree of calcification. 4 kinds of pericardial xenografts, group I [Xenomedica, equine pericardial xenografts], group II [0.625% glutaraldehyde-preserved bovine pericardiums], group III [0.5% Triton X - 100 treated bovine pericardiums], and group IV [1.2% Triton X - 100 treated bovine pericardiums] were implanted in subcutaneous layer of growing rabbits, and they were explanted about 3 months later. The mean calcium contents[%/mg of dry tissue] of 0.5% and 1.2% Triton X - 100 treated bovine pericardiums [80.0$pm$27.1%: 78.6$pm$47.0% respectively] were lower than those of glutaraldehyde-preserved bovine pericardiums[126.2$pm$29.8] [p=0.05]. Thus, under the conditions of subcutaneous implantation in rabbits, Triton X - 100 was efficient in calcification mitigation.