The ability to generate transgenic mice that express exogenous genes, express genes in a tissue specific manner, or do not express an endogenous gene will dramatically impact nutritional studies. Use of transgenic animals will greatly expand the types of experiments that can be performed, for example, by permitting researchers to examine specific mechanisms underlying nutritional relationships. These studies can be viewed from two perspectives; the effect of nutrition in general or nutrients in specific on the regulation of gene expression; and conversely, the effects of gene expression upon nutrient utilization or other aspects of metabolism. In addition, transgenic animal models have been and can be established to characterize human pathologies, e.g., pituitary gigantism or atherosclerosis, and the roles and interactions of nutrition in these and other metabolic diseases may then be evaluated. The use of transgenic animals in nutrition research is new and quite fertile, and exciting results will continue to surface.