It is generally agreed that fluorine is a constant component of enamel and dentin and that of all structures in the body, the teeth probably contain the largest amount of this element. In spite of efforts extending over the last 130 years no agreement has been reached as to the actual amount of fluorine in enamel and dentin. McClure (9) reviewed the literature of the period 1803-1933 and found the reported fluorine content of enamel, dentin and whole teeth to vary from zero to 1.4 per cent. Jacob and Reynolds (7), whose work was not reviewed by McClure, found whole teeth to contain 1.8 to 3.5 per cent fluorine. Of the older reports most credence has been placed in the results of Gautier and Clausmann (6) who found the fluorine content of enamel to vary between 0.118 and 0.172 per cent. It was McClure's opinion that the creditable literature indicated the presence of 0.1 to 0.2 per cent fluorine in enamel.The analyses made since McClure's review have indicated a lower fluorine content of teeth and teeth structures than had been found by the older investigators. The recent improvements in fluorine analytical methods have resulted in a downward trend of the determined amounts of fluorine in biological materials. Klemet (8) found enamel and dentin to possess an identical fluorine content, namely 0.05 per cent. Bowes and Murry (3) reported enamel to contain 0.02 per cent fluorine. They (4) later found mildly mottled teeth to contain 0.035 per cent fluorine in the enamel and 0.07 per cent in the dentin.