The rate of dissolution of beta-tricalcium phosphate (beta-Ca-3(PO4)(2); beta-TCP) has been measured in the solution system Ca(OH)(2)H3PO4-NaOH-HNO3-H2O. The effects of different parameters such as pH, temperature, time, and saturation have been investigated, At zero saturation, the logarithm of the dissolution rate is a linear function of the pH (log(j(0)) = 2.02 - 0.82 pH; r(2) = 0.993; in mmol/m(2)s), indicating diffusion-limited dissolution, A simple calculation of the theoretical rate of a diffusion-controlled process showed that our data are consistent with theory, Moreover, the activation energy for this process is low (E-act = 3.9 kcal/mol) also suggesting that the beta-TCP dissolution is controlled by diffusion processes, At increased saturation, the initial beta-TCP dissolution rate decreases much faster than that predicted assuming a diffusion-controlled model, However, this latter model gives a good prediction of the results if it is assumed that beta-TCP dissolution is controlled by the dissolution of an interfacial layer of hydroxyapatite (Ca-5(PO4)(3)OH;HAp) : log(j)= -1.47 + 1.34 log(1 - S-HAp); r(2) = 0.959. The beta-TCP dissolution rate decreases very sharply with time, This effect increases at higher pH or saturation, Several explanations are proposed and discussed, even though none is conclusive.