Contact angle measurements were employed so that we could study the wetting properties of human whole saliva and saliva substitutes containing mucins or carboxymethylcellulose (CMC) on human oral mucosa (in vivo) and on ground and polished human enamel (in vitro). A new approach was introduced for measuring contact angles on human oral mucosa in vivo. It was shown that the wetting properties of CMC- and mucin-containing saliva substitutes on human enamel were significantly better than those of human whole saliva. On human oral mucosa, the wetting properties of CMC-containing saliva substitutes and human whole saliva were comparable, but were surpassed by those of the mucin-containing saliva substitutes. Mucin-containing substitutes thus provide good wetting properties on ground and polished enamel as well as on oral mucosa.