Slightly de-calcified enamel chips were treated with a 2% solution of SnF2 containing radioactive tin as SnF2 and were then inserted into partial dentures of two volunteers. A follow-up of the radioactivity of the enamel showed that after a 20% decrease within the first four days in the mouth no appreciable amounts of tin were lost during the following four mo. Apparently decalcified enamel holds tin from topical applications of SnF2 very tightly over a long period of time under the conditions which exist in the human mouth.