Fluorine can be analysed by proton activation, with detection of prompt gamma-rays. Using external beams, it is possible to make in vivo determinations and to follow the fluorine concentration in fluoridated enamel. Radiation damage and the radiation hazard are investigated. It is found that the dose rate is very small and that the technique can be used without radiation hazard. Local destruction on the enamel surface is investigated using a scanning microscope; no modification is observed in the crystallite structure after irradiation.