The purpose of this study was to evaluate mechanisms of mineral homeostasis and mineralization in term infants with recommended vitamin D intakes. Infants fed human milk (nine), cow milk-based formula (11), or soy-based formula (11) were studied at 2 weeks and at 2, 4, 6, 9, and 12 months of age. While receiving 400 IU of vitamin D, all infants maintained serum vitamin D concentrations higher or equal to normal adult concentrations, and serum 25-hydroxyvitamin D levels were maintained at or above normal adult levels. Serum 1,25-dihydroxyvitamin D concentrations were higher than those of adults in the formula-fed but not in the human milk-fed infants. Serum calcium and phosphorus values were similar in all groups; however, urine phosphorus excretion and urine calcium excretion were adjusted to intakes. Serum parathyroid hormone values were normal in all groups. Bone mineral content significantly increased with age similarly in all groups; however, an apparent plateau occurred at 6 months of age in all groups. Bone width steadily increased with age. Taken as a whole, these data suggest that the vitamin D-sufficient term infant fed human milk, cow milk-based formula, or the soy-based formula studied can regulate mineral metabolism within acceptable physiologic limits to attain similar levels of serum minerals and bone mineral content.