Polychlorinated biphenyls (PCBs) and dichlorodiphenyl trichloroethane (DDT) are the most frequent chemical contaminants present in human milk. Factors involving the levels of PCBs and DDT in human milk are revised. Allowable daily intake of both contaminants is indicated as well as their effect on human exposure are discussed. Since available data suggest that these contaminants are available for redistribution to the lactating mammary gland, we stress the importance of a dietary regimen to breast fed mothers in order to prevent the mobilization of body fat stores for milk fat synthesis.