A review of the literature provides support for the concept that maternal nutritional status has a significant influence on embryonic and fetal development. The consumption of `poor’ diets has been shown to be a risk factor for poor pregnancy outcome, while the provision of selected nutritional supplements prior to and during pregnancy has been associated with improved pregnancy outcome. Despite the above, it has been difficult to identify specific nutrient deficiencies as causative factors of abnormal development. One explanation for this failure is that embryo/fetal nutritional deficiencies can arise through a number of mechanisms in addition to a low maternal intake of a nutrient(s). Evidence is presented for the hypothesis that the developmental toxicity of a number of teratogens can be ascribed, in part, to their ability to induce alterations in the partitioning of essential trace elements between the maternal and fetal unit. An implication of the above hypothesis is that maternal diet can be an important modulator of the developmental toxicity of several agents.