In a clinical study 12 healthy volunteers consumed a standardized basal diet consecutively supplemented with either sucrose (6 days, 80-100 g/day) or xylitol (18 days, 40-100 g/day). Pre- and post-periods with normal diet were also included in the study. With the exception of a few cases of diarrhoea at the start of the xylitol administration no other clinical signs indicated treatment-related side-effects. Whereas during the xylitol period plasma cholesterol values tended to be decreased, triglyceride levels remained unaffected. Other parameters (such as urinary calcium and oxalate as well as plasma uric acid) which have been suggested to be influenced by carbohydrate consumption were in fact not altered by the dietary regimen of the present study. A variety of other serum and urinary parameters revealed also no between-treatment differences. It may be concluded from these data under the present experimental conditions that subchronic consumption of considerable doses of sucrose and xylitol respectively reveals no relevant changes of a variety of clinical parameters which would indicate any kind of metabolic intolerance to these sweetening substances.