A number of solutions used for topical application and mouth rinsing were analyzed and calcium fluoride formation on human enamel at 20 °C determined. In most solutions free fluoride and hydrogen fluoride were the main ion species, whereas stannous hydroxide and stannous fluoride ion pairs were the dominating components of stannous fluoride solutions. The calcium fluoride formation on enamel was assessed by chemical analysis. It was found that an increase in fluoride activity and a decrease in pH increased the calcium fluoride formation to almost the same extent