Intakes and excretions of calcium, magnesium, iron, and silicon were determined for 12 men consuming controlled diets containing fruits and vegetables (high fiber diet) or fruit and vegetable juices (low fiber diet) for periods of 26 days. Magnesium and iron were added to the low fiber diet to make the two diets as equivalent as possible in these respects. Mean daily intakes on the low and high fiber diets, respectively, were: calcium, 1070 and 1166 mg; magnesium, 355 and 322 mg; iron, 21.8 and 26.4 mg; silicon, 21.6 and 45.8 mg. Mean daily balances on the low and high fiber diets repectively, were: calcium +72 and -122 mg; magnesium, +28 and -32 mg; iron, +3.8 and +4.6 mg; silicon, -3.5 and -14.6 mg. Calcium magnesium, and silicon balances were significantly lower on the high than on the low fiber diet (P less than 0.01).