Ovarian and testicular steroids have important effects on body weight and composition in rats. Estradiol and testosterone decrease adiposity, while progesterone increases carcass fat content. These hormone-induced changes in body weight and composition are accompanied by changes in food intake and voluntary exercise, suggesting that the hormones induce behavioral changes which alter body weight and adiposity. However, several lines of evidence indicate that these behavioral changes are neither necessary nor sufficient to produce the hormone-induced body weight shifts. Rather, peripheral metabolic effects of gonadal steroids may be of primary importance in the control of fat disposition. Steroid effects on triglyceride clearance from circulation, along with changes in hepatic synthesis, may in turn alter the availability of triglycerides as an oxidizable fuel, contributing to the changes in food intake. From this perspective, estradiol- and progesterone-induced changes in food intake are viewed as consequences, rather than causes, of changes in fat metabolism. It is suggested that during naturally-occurring reproductive states gonadal steroids interact with other hormones, such as prolactin, to partition available triglycerides among tissues which oxidize, excrete or store long-chain fatty acids (e.g., striated muscle, mammary gland, or adipose tissue, respectively).