The effect of peroral administration of xylitol (5% or 20% in food) on adrenal function was investigated in thirty-five Long-Evans male rats. The control rats were fed either a non-substituted stock diet or a 20% glucose diet. Glucose elevated and 20% xylitol reduced the growth of the rats (P less than 0.001), but 5% xylitol had no effect on the body weight. The concentrations of serum glucose and lactic acid decreased in rats fed 20% and 5% xylitol, respectively, but those of insulin, glucagon, corticosterone and aldosterone were not affected. In the adrenal glands, 20% xylitol loading was associated with increased epinephrine (P less than 0.05) and norepinephrine (P less than 0.001), but with decreased aldosterone (P less than 0.001) concentrations. The weights and histological picture of adrenal glands were normal. The urinary pH of xylitol-fed rats decreased significantly (P less than 0.01). Although peroral xylitol affected the levels of aldosterone and catecholamines, a normal glucocorticoid metabolism was permitted. The reduced aldosterone levels were regarded as secondary reactions, possibly resulting from alterations in electrolyte and/or acid-base balance. The increased catecholamine synthesis may be associated with the promoting effect of xylitol on intestinal calcium absorption.