as the control and study of bone disease, arteriosclerosis, Hitherto, most discussions of nucleation phenomena have been arthritis, gall and kidney stone formation. Most crystallizaconcerned with the condensation of vapors. In this paper, thermotion theories in aqueous solutions, however, have been dedynamic arguments are presented to show that such classical nurived, without thermodynamic verification, ''by analogy'' to cleation models are inadequate for interpreting nucleation in aquetheories for the kinetics of phase transitions in molecular ous media. The use of the Young equation involving force balance systems. Such an approach yields data that are difficult to solutions is applicable only for uncharged interfacial systems. To reconcile with experience. Thus, the surface free energy avoid the involvement of a contact angle concept, which provides (surface tension) of hydroxyapatite (HAP) derived from little kinetic information about heterogeneous nucleation, the presclassical heterogeneous nucleation theory ranged from 100 ent paper is concerned with the use of interfacial measurements to calculate the rates of these reactions. The method is illustrated to 331 mJ/m 2 , based on the rate or induction time for HAP by calculation of a rate of heterogeneous nucleation of hydroxyapcrystal nucleation/growth on proteins (elastin, collagen) and atite at elastin surfaces (4.4 1 10 08 mol min 01 m 02 ) that is close amino acids (7, 8). Ignoring the influence of serum macroto the value, 3.9 1 10 08 mol min 01 m 02 , reported in the literature. molecules, this would result in such a large interfacial ten-