By means of the Warburg technique it was studied whether addition of xylitol interferes with sucrose degradation in human saliva. For this purpose, different concentrations of xylitol were added to incubated saliva-sucrose samples. An inhibition of sucrose degradation was not obtained under both aerobic and anaerobic conditions. Therefore, it seems to be of doubtful value to produce, e.g., sweets consisting of a sucrose-xylitol mixture and to expect that these products will have caries-preventive properties.