The aim of this in vitro study was to examine whether the concentration of amine fluoride solution influences the uptake of fluoride by enamel after topical treatment. Four slabs were prepared from each of 31 impacted third molars and selected at random so that one slab from each tooth was present in each group. One group of slabs served as an untreated control (D). The slabs of the other three groups were shaken for 3 min in an amine fluoride solution on 3 successive days: group A (1% F), group B (0.5% F) and group C (0.25% F). The amounts of KOH-soluble fluoride produced with 1 and 0.5% amine fluoride solution did not differ significantly and were superior to 0.25% amine fluoride solution. A statistically significant increase in structurally bound fluoride was observed in groups A, B and C compared with control group D. The difference in the amounts of structurally bound fluoride was significant only between 1 and 0.25% F concentrations. These data suggest that the fluoride content in an amine fluoride solution (1%) can be decreased by half without reducing its ability to form alkali-soluble or structurally bound fluoride. The results of this study are consistent with those of previous clinical studies.