Simulated body fluid (SBF) solutions are widely used for in vitro bioactivity tests and to coat bioinert materials with biomimetic calcium phosphates. In this study, a SBF solution was used to precipitate hydroxy carbonated apatite (HCA) with a general formula Ca10-x(HPO4)(x-y)(CO3)(y)(PO4)(6-x)(OH)(2-x) on a bioactive titanium surface. X-ray diffraction (XRD) as well as cross-sectional transmission electron microscopy (TEM) analyses revealed that the biomimetically derived crystallites show a preferred growth orientation in direction of their c-axis and perpendicular to the surface of the bioactive substrate. This growth behaviour as well as the measured crystal dimensions ranging from 5 x 10 x 20 to 5 x 20 x 100 nm are very similar to that found in the mineral part of mammalian bone, where the c-axes of plate-shaped apatite crystals are well aligned with the long axes of the collagen fibrils. (c) 2007 Elsevier B.V. All rights reserved.