The requirements for zinc during lactation are greater than those during pregnancy, especially during the early weeks postpartum. Therefore, lactation poses a significant threat to maternal zinc homeostasis, particularly in populations with chronically low dietary zinc intakes. The current knowledge of maternal zinc status in lactation, particularly in developing countries, is reviewed herein with emphasis on the effects of zinc supplementation trials. The studies that have examined the zinc status of breast-fed infants are also reviewed.