Polyanionic proteins of calcified tissues have been postulated to provide calcium ion-binding sites which initiate mineral formation, even though it is known that such proteins in solution may inhibit apatite induction and growth. In the studies reviewed here, it was shown that minute amounts of non-collagenous macromolecules from dentin and bone, such as phosphoprotein and proteoglycan, are capable to induce apatite at physiological ion concentrations in vitro, when immobilized on a stable support.