1. Stannous fluoride toothpaste was used twice yearly for three years in supervised brush-ins by puplis at two Melbourne schools--one coeducational and one boys. 2. Of the original 492 pupils who formed the Test and Control Groups, 347 were available for the final examination. Of these, only the Test Group (167) had participated in four brush-ins. 3. The Test Group consisted of 119 boys and 48 girls, and the Control Group 129 boys and 51 girls. 4. The reduction in caries increment was 16 per cent for DMFS and 19 per cent for DMFT. A reduction of 34 per cent DMFS and 30 per cent DMFT was recorded for the girls. 5. The results for boys in the co-educational State school showed no reduction in caries increment. 6. Time taken for the brush-ins was not more than 20 minutes.