The caries preventive outcome of a school-based program with salivary; lactobacillus counts as sugar-motivating tool was evaluated in six cohorts of totally 936 adolescents in a comprehensive school in Sweden. Students from a neighboring district with similar socioeconomic structure but with no corresponding dental health-promoting activities were selected as reference. The program started in the beginning of the 7th grade (13 years) and was terminated at the end of the 9th grade (16 years). Salivary lactobacilli were evaluated semi-annually with a dip-slide method and used for individual counseling. Dental caries was scored from the dental records and bitewing radiographs of each 4th participant at baseline and at 16 and 19 years of age. The number of salivary lactobacilli decreased significantly (P