Bawden, J.W., Wennberg, A. Hammarström, L. In vivo and in vitro study of5 9Fe uptake in developing rat molars.Autoradiographic methods were used to study59Fe uptake in vivo in mineralizing tissues of young rats. Localization of5 9Fe was observed in the ameloblastic layer of molars. In vitro studies were performed which demonstrated that5 9Fe uptake in developing rat molar enamel was limited by the metabolic activity of the cells of the enamel organ.