A cup of tea (containing about 0.49 mg F) containing soluble fluoride in the optimum necessary amount was recommended after every school lunch to 298 school children of Suhara in Sumon, Niigata prefecture, for about 250 days from December, 1975 to November, 1976. Increment lesions which appeared at three carious predirective sites, i. e., pits and fissures, proximal, and free gingival smooth surfaces of the children of the test school in the Suhara district were compared to the lesions found at the same sites in 185 children of three control schools in the Kamijo district of the same village. Reduction rates at each site were 52.8% for the pit and fissures and 57.2% for the proximal sites, but there was no reduction at the free gingival sites.