The rehardening properties of four saliva substitutes on artificially softened human enamel have been investigated by microhardness measurements. The saliva substitutes were all based on the same formula, containing calcium, phosphate and fluoride as the main electrolytes, and mucin or carboxymethylcellulose as the main macromolecules. It has been shown that a rehardening potential exists in the saliva substitutes when calcium and phosphate are present. Omitting F− greatly reduces the rehardening potential. The rehardening is better in case of the CMC‐containing saliva than in that containing mucin.