The fluoride uptake from six different fluoride solutions applied to the buccal surfaces of extracted, newly erupted premolars was measured. The fluoride concentration of two symmetrically situated areas were compared at various distances from the enamel surface after treatment of one of the areas with a fluoride solution. Exposure of enamel to sodium fluoride, acidic phosphate fluoride, monofluorophosphate, stannous fluoride, sodium hexafluorostannate and cetylaminhydrofluoride was found to produce significant but widely variable increases in the fluoride content of the superficial layers. The uptake of fluoride from all test solutions, except cetylaminhydrofluoride appeared to be confined mainly to the outermost 10–15 μm of enam