Zinc is a micronutrient which is critical to normal growth and development. Zinc concentrations in human milk decline sharply during the early months post partum, regardless of maternal zinc intake. Milk zinc concentrations do not increase in response to increased maternal zinc intake if maternal zinc status is adequate. The mechanism of zinc secretion into milk is not fully understood. A mutation in the gene for a zinc transporter protein may account for abnormally low milk zinc concentrations associated with severe zinc deficiency in breastfed infants. The zinc requirements of breastfed infants are generally met with exclusive breastfeeding through 5-6 months of age, due to the favorable bioavailability of the zinc in human milk. Because of declining milk zinc concentrations and intake, zinc status in exclusively breastfed infants is likely to become marginal beyond 6 months of age, and may become suboptimal for some infants if exclusive breastfeeding continues. The choice of complementary foods is important to maintain adequate zinc status in breastfed infants after 6 months.