AbstractTwo experiments tested the effects of xylitol or sucrose‐containing chewing gums on plaque formation. In the first experiment the 18 subjects maintained their normal dietary habits, and in the second they received a sucrose‐free diet during the 3‐day experimental periods. Plaque formation was assessed gravimetrically and/or planimetrically. When the dietary habits were not altered, neither the sucrose nor the xylitol‐containing chewing gums had significant effects on the plaque scores. When sucrose was almost eliminated from the diet, plaque formation was significantly higher in the sucrose than in the xylitol and the placebo groups. Although plaque formation was lower in the xylitol group than in the placebo group, the differences were not statistically sign