The study will be a metabolic balance study of breast milk consumption and three dose-response cross-over arms of iodine enriched infant formula milk in 60 healthy 2-3 mo old infants (30 breast fed and 30 formula fed). Breast fed infants will be exclusively and unrestrictedly breast fed by the mother and the breast milk consumption will be monitored for 4 days by weighing the infants before and after each feeding session. Formula fed infants will be randomly allocated to three 11 days cross-over periods of exclusive consumption of infant formula milks (IFM) providing 60 µg I/day, 110 µg I/day and 220 µg I/day. The iodine intake will be monitored by recording the amount of infant formula milk fed to the infants. The iodine excretion will be measured from complete collections of urine and feces for a 4-day period for each arm. The iodine retention will be calculated from the difference between measured iodine intake and excretion. Analytical determination of the iodine content in biological samples will be done by mass spectrometry after digestion and iodine extraction. The sample size is based on an estimated dose-response of the different levels of dietary iodine on iodine excretion.