Iron balance studies were performed in 17 full term male infants from their 3rd until their 17th week of life. The balance studies were made in the infant's home and comprised 5 periods with an interval of 3-4 weeks, each consisting of three 24-hour collections. Ten infants were breast-fed, 3 received an adapted infant formula (P1, iron content 1.1 mg/l) and 4 were given the same formula enriched with iron, copper and zinc (P2, iron content 10.35 mg/l). From the 3rd to the 17th week of life the breast-fed infants got a mean iron intake of 0.2 mg/kg body weight X 3 days and they retained 0.09 mg/kg b.w. X 3 days. The P1 group received 0.48 and 0.47 mg/kg b.w. X 3 days and retained -0.01 and -0.5 mg iron/kg b.w. X 3 days, while the P2 group had an intake from 5.04 to 6.38 mg b.w. X 3 days and retained between 1.13 and 3.66 mg iron/kg b.w. X 3 days. Comparing the 3 groups it can be concluded that the P1 group retained definitely less iron than the breast-fed group, whereas the P2 group retained 12 to 40 times more iron than the breast-fed babies.