This study measured the fluoride in tooth enamel of 338 schoolchildren after daily use of acidulated phosphate-fluoride (APF) tablets, and investigated the relationship between observed amounts of enamel fluoride and incidence of caries. Randomly selected study groups received under supervision either one placebo tablet, one APF tablet containing 1 mg fluoride, or 2 APF tablets (3 hours apart) each school day. An abrasive enamel-type biopsy of a maxillary central incisor was taken 30 months after the start of fluoride tablet treatments at the time of the follow-up examinations. Mean fluoride levels in the biopsied enamel from each of the three groups were similar despite a significant restriction in caries in the group receiving two APF tablets per day. These findings suggest that fluoride can restrict dental caries by some mechanism other than fluoride uptake in the enamel.