This study was undertaken to reveal detailed changes in fluoride distribution at different developmental stages of upper incisor enamel under various fluoride administration regimes. Four groups of Wistar rats received water containing 0, 25, 50 and 100 parts/10(6) fluoride respectively for 10 weeks. Five different enamel specimens were removed from the developing enamel, excluding the matrix-formation stage. Fluoride distribution in each specimen was analysed from the surface to the enamel-dentine junction using an abrasive microsampling technique. Fluoride concentration was invariably highest at the surface and decreased sharply towards the interior at every site in both control and experimental groups. The concentration throughout the tissue increased with fluoride intake at each stage of development. The fluoride-gradient curves were similar at each of the different sites of tooth development. However, the fluoride concentration of the enamel interior was significantly higher at early maturation than at the other four sites.