Effects of dietary lactose and a lactase preparation on the intestinal absorption of calcium and magnesium were studied in 3 groups under 8 months of age; infants on a proprietary milk, infants on a lactose-free milk, and infants on a proprietary milk to which a lactase preparation was added. The intestinal absorption of both elements was reduced in infants on a lactose-free milk and enhanced in infants who were fed on a proprietary milk and given a lactase preparation.