A laboratory study was carried out to evaluate the effectiveness of NaF and SnF2, when incorporated into zinc oxyphosphate cement, in reducing the solubility and increasing the microhardness of human enamel. The control cement contained no added fluoride, and the test cements were prepared to contain fluoride concentrations of either 1,000, 2,000, or 4,000 ppm from each of the two test fluorides. SnF2-containing cement provided significantly (P < .01) greater solubility reduction at all three concentrations than did NaF cement. SnF2 was also more effective than NaF in rehardening enamel surfaces. SnF2 is thus much more effective than NaF when added to orthodontic cement. Current topical treatment literature, both laboratory and clinical, is in accord with this conclusion.