Dental students (n = 31) with either high salivary lactobacillus count (greater than 10(4) CFU/ml) or high salivary sucrase activity (greater than or equal to 10 mumol/min X mg protein X 10(-3), or both, were selected to participate in this dietary experiment. For 2 weeks the students avoided sucrose in their diet. Stimulated saliva samples were collected before and after the diet. An additional follow-up sample was collected after 2 weeks of normal diet. The lactobacillus count of undiluted saliva was determined by the Dentocult dip-slide technique. The sucrase activity was determined spectrophotometrically by measuring the sucrose-cleaving activity of centrifuged saliva supernatant. Both the reduction in dietary sucrose and the return to normal diet caused a significant change in these values.