Studies have been conducted on various metabolic characteristics of lean and obese Pima Indians, including studies of fat-cell morphology, glucose transport, and lipolysis; lipoprotein lipase activities; sodium-potassium ATPase in red cells, adipocytes, and fibroblasts; lipids and lipoprotein metabolism; fatty acid metabolism; and sterol balance. Insulin concentrations, insulin binding, insulin action on glucose disposal, fatty acid metabolism, and islet function were compared in lean and obese individuals, and the relationship between insulin resistance and muscle morphology was explored. To explore potential abnormalities in energy balance, calorie intake and gastric emptying were compared in lean and obese Pimas and measurements of energy expenditure were performed. The data suggest that there are multiple metabolic differences that accompany obesity in Native Americans. A lower metabolic rate was a determinant of future weight gain, and abnormalities in use of free fatty acids and cell insulin action were suggested, which emphasize the need for further studies in these areas.