Breast-fed infants are dependent on an adequate supply of minerals and trace elements for normal growth and development. For most of these elements, the mammary gland appears to have developed mechanisms to regulate their concentrations, even when the maternal diet varies considerably or maternal conditions are affected by different challenges. For some elements, however, there appears to be little or no such regulation. Increased knowledge about these mechanisms, or their absence, and to what extent they may compensate for adverse maternal conditions, including poor nutrition, will help identify infants and women at risk for deficiencies of these nutrients.