Proton activation analysis, using the reactions 19F(p, alpha gamma)16O and 15N(p, alpha gamma)12C, was employed to study the fluorine and nitrogen content of developing rat molar enamel at various stages of maturation. Four groups of rats were utilized: Group I -- injected intraperitoneally at 6 days of age with 20 mg F/kg b.w. as sodium fluoride solution and terminated at 30 minutes and 1, 5 and 9 days postinjection; Group II -- injected in a similar way at 7 days of age and terminated 30 minutes and 1, 4 and 8 days postinjection; Group III -- injected with 10 mg F/kg, at 6, 15 and 19 days of age and terminated 30 minutes later; Group IV -- control animals injected with distilled water at 6 and 15 days of age respectively and terminated 30 minutes later. Analysis reflected decreasing nitrogen content in the enamel as maturation proceeded. However, fluorine concentrations were highest in all groups at the earlier stages of enamel development.