Examples are presented in interactions between genetic factors and certain trace during development in experimental animals. One type of interaction irenatal nutritional manipulation. The other involved strain differences, which lead differential responses to dietary deficiency. The mutant gene pallid in mice produces abnormal development of the inner ear similar to that resulting from intrauterine manganese deficiency. This abnormality is prevented by manganese supplementation of prenant mutant mice, and as in manganese deficiency, appears to result from depressed synthesis of mucopolysaccharides. Are interaction between copper and the mutant gene cribkled in mice is describes. High dietary copper curing prenatal and abnormal life doubled postnatal survival of mutants and brought about alterations in other parameters. In A/J mice, which have a significant incidence of spontaneous cleft lip and palate, a marginal deficiency prenetally of dietary zinc did not cause an increased incidence of this anomaly. However, the incidence of other malformations was greatly increased in this strain but not in hybird controls. It is proposed that in man as in animals teratogenesis might involve genetic-nutritional interactions as well as multifractorial interactions including genes, nutrients, drugs, and other environmental agents.