A detailed comparative study of the mechanochemical transformation of two mixtures: Ca(OH)(2)-(NH4)(2)HPO4 and Ca(OH)(2)P2O5, milled in a mortar dry grinder for different periods of time was carried out. The phase transformations obtained at each milling stage were studied by X-ray diffraction, infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry and thermogravimetric analysis. The transformations taking place during the first periods of milling are very different for both mixtures. However, prolonged milling, over nearly the same period, causes amorphization of both mixtures. DSC analysis of the milled powders showed the temperature of crystallization of hydroxyapatite and tricalcium phosphate (beta-TCP). Calcinations of all the different milled powders at 800 degrees C for 2 h, results in the formation of hydroxyapatite and beta-TCP (C) 2006 Elsevier Ltd. All rights reserved.