The major objective is to elucidate the role of early nutritional experiences on the developmental aspects of carbohydrate and the subsequent effect on adult adiposity and muscularity. Three varieties of genetic obesity are being used. The obese hyperglycemic mouse (ob/ob), the yellow obese mouse (Ay/a), and the fatty rat (fa/fa). These animals are being studied from the preobese phase of developmemt through fully blatant obesity. Currently, methods are being refined for the early identification of the fa/fa genotype, prior to the expression of obesity. The effects of postweaning dietary carbohydrates and fat on oxygen consumption and body composition have been evaluated. During the preobese and subsequent phases of development, the major sites of lipogenesis and enzymatic profiles of liver and adipose tissue will be evaluated to ascertain whether the major site of lipogenesis shifts from liver to adipose tissue as development proceeds. Additionally, investigations are proposed to determine whether an intrinsic defect exists in the musculature of these animals, which may effectively limit the availability of energy utilization for muscle growth. The results of these investigations should increase our understanding of the interaction of early dietary experiences and neonatal development, particularly with regard to the development of obesity.