Heat treatment was expected to enhance the long-term reliability of hydroxyapatite (HA) coatings on metal substrates. In this study, factors influencing phase compositions and structure of plasma sprayed hydroxyapatite coatings during heat treatment were carefully analyzed. The phases were characterized by using X-ray diffraction (XRD), the OH-ion contents were determined by Fourier transform infrared (FTIR) spectroscopy. Of the involved factors, beating temperature is of more importance. The appropriate heat treatments is (600-700 degreesC) x 2 h for coatings made from fine particles (10-20 mum) and 600degreesC x 2 h for coatings made from coarse particles (50-80 mum). The excessive high temperatures and long holding times were unfavorable for the structural integrity of HA. (C) 2002 Published by Elsevier Science B.V.