• An adequate supply of calcium is important for normal bone mineralization in infants. Special infant formulas have been developed to treat infants with a high risk of developing allergy. Similar to other diets, it is important that these products are nutritionally adequate. We have measured calcium retention from a new formula based on whey hydrolysate and compared it with conventional formulas, using extrinsic labeling with calcium 47 and the weanling rhesus monkey as an animal model. Retention of calcium was similar for all formulas studied: 45% ± 4% (mean ± SEM) from whey-hydrolysate, 47% ± 2% from whey-predominant, and 53%±7% from casein-predominant formula. Calcium retention from human milk, 72%±3%, was significantly higher than from formula. Using these retention values and the calcium concentrations of the diets, infant formula and human milk deliver approximately equal amounts of calcium to the infant.