In 40 rabbits (white Ncw-Zcalanders) studies were performed to evaluate whether the insufficiency of the adrenocortical system induced by dexamethasone may be prevented by simultaneous xylitel intake. Corticosterone and cortisol were determined in the serum by means of a double isotope method before and after the examination. Furthermore, the stimulation of the adrenal cortex by fl-1-24 corticotrophin was tested. The sole intake of sorbitol or xylitol results in neither morphological nor functional disturbances of the adrenal cortex. The group having been given sorbitol and dexamethasone revealed a marked insufficiency of the adrenocortical system and partial adrenocortical atrophy. The group receiving xylitol and dexamethasone did not show any functional or morphological changes of the adrenal cortex. So, the conclusion may be drawn that the adrenocortical insufficiency induced by dexamethasone can be prevented by the simultaneous administration of xylitol in rabbits.