Inverted phase-contrast microscopy has been successfully used to observe in situ the growth of hydroxyapatite (HAp) from pseudophysiological solution under dipalmitoylphosphatidylcholine (DPPC) monolayer. The results showed that the DPPC monolayer template could control the sizes, orientation and morphology of the formed HAp crystals effectively. The HAp spherical particles with the diameters of 0.4-0.8 mum were formed beneath the DPPC monolayer after 7 days. The structure and component of HAp were investigated by transmission electron microscopy and electronprobe microanalyzer. The HAp crystallization process is controlled predominantly by electrostatic interactions between the template and HAp. (C) 2003 Elsevier B.V. All rights reserved.