Moderate obesity (17% excess body weight) was induced in female rats by offering a "cafeteria" diet during 82 days. The adaptive changes in five amino-acid-metabolism enzymes were determined in liver and white- and brown adipose tissues by comparison with chow fed controls both in the fed and 24-h starved states. Plasma urea levels were lower in the obese and the changes in enzymatic activities pointed to a lower rate of amino-acid metabolism in our dietary obesity group. The levels of activity of amino-acid-metabolism enzymes in brown adipose tissue were higher than in white adipose tissue and in most cases comparable to that of liver. The importance of amino acids as a fuel source in brown adipose tissue thermogenesis cannot be ruled out.