X-ray diffraction analyses, and Sr89 and Ca45 uptake studies in tibiae and incisors of control and fluoride treated one-year-old rats were carried out. In the tibia ends and shafts an improvement of bone apatite crystallinity in the direction of the a axis and not the c axis was produced by fluoride ingestion. No changes in incisor apatite crystallinity were observed. Uptake of Ca45 and Sr89 was decreased in the tibia ends of the 25 and 50 ppm F treated animals. Sr89/Ca45 ratios in the tibia samples were the same as in the serum specimens. There was a discrimination against Sr in relation to Ca in the incisor bases. Radioactivity in the tibia of one-year-old animals was 1/40 to 1/50 of that found in a group of young animals treated similarly in an earlier experiment. In the young rat the tibia ends were found to incorporate more Sr89 and Ca45 than the incisor, while the opposite was found in the older rats.