In vivo studies in the rat during the weaning period and in vitro studies on cultured cells have shown that nutriments and pancreatic hormones play a major role in lipogenic enzyme gene expression in liver and adipose tissue. Activation of lipogenic enzyme gene expression in liver and adipose tissue is dependent upon the increased supply of glucose and the concomitant hyperinsulinemia that occur after weaning. In contrast, an elevated supply of polyunsaturated or an increased plasma glucagon level prevent lipogenic enzyme gene expression in liver and adipose tissue. Glucose-6-phosphate seems to be the intracellular metabolite that mediates the transcriptional activation of lipogenic enzyme genes in response to glucose.