The purpose of the study was assessment of the influence of locally applied acidified fluoride solutions on the condition of teeth of school children living in a town district with fluoridated drinking water and in another district without fluoridation of drinking water. Acidified fluoride solutions were applied locally by brushing--5 procedures at two-week intervals in the first and second year of the experiment. The condition of teeth was assessed calculating the indices CMF and CMFp. In the light of the obtained results it may be said that the externally applied acidified solutions of fluorides had an approximately evident effectiveness in prevention of caries both in children drinking fluoridated or non-fluoridated water.