Obesity in the Pima Indian is associated with a massive increase in adipose tissue mass (25-50% of total weight). The increased fat mass is due to both an increase in adipose cell size and cell number. Adipose lipoprotein lipase activity increases with obesity and is correlated with adipose cell size. Methods of studying various parameters of carbohydrate and lipid metabolism have been established using isolated human adipocytes and membrane vesicles and will be used to study human obesity.