Intact and adrenalectomized (ADX) rats were mildly food deprived and administered dexamethasone (type II agonist), aldosterone (type I agonist), corticosterone (mixed agonist), or vehicle 24 and 2 h prior to forced exercise in a treadmill. The endurance of intact animals was unaffected by hormone treatments. Adrenalectomy greatly advanced the onset of fatigue, and aldosterone exacerbated the effect of adrenalectomy. Corticosterone improved endurance in ADX rats, and dexamethasone was even more potent in this respect. Aldosterone slowed deprivation-induced weight loss in ADXs, while corticosterone and especially dexamethasone accelerated loss. Thus, endurance was directly related to body weight loss, and presumably to the fuels released by such loss. The results extend the type I-type II functional dichotomy to the delivery of utilizable energy for metabolically active tissues.