The heterogeneous nucleation of calcium phosphates including octacalcium phosphate (Ca4H(PO4)(3). 2.5H(2)O), hydroxyapatite (Ca-5(PO4)(3)OH, HAP), and fluorapatite ((Ca-5(PO4)(3)F, FAP) on anatase and rutile surfaces has been studied in solutions supersaturated with respect to each phase. Induction periods preceding the initial crystal growth of the calcium phosphate phases varied markedly with relative supersaturation, At the same relative supersaturation, the induction time for calcium phosphate nucleation on anatase surfaces was much shorter than that on rutile surfaces. The surface properties of these titanium oxides were characterized by zeta-potential measurements and by contact angle measurements involving a thin layer wicking technique. The major difference between the surfaces was in the Lewis base surface tension parameters, gamma(s)(-), 48 and 16 mJ m(-2) for anatase and for rutile, respectively.