Depending on the coating method utilized and subsequent heat treatments (such as through the use of plasma-spray deposition), inter-diffusion of atomic species across titanium (Ti) and hydroxyapatite (HA) coatings may result. These events may lead to structural and compositional changes that consequently cause unanticipated HA phase transformations which may clearly influence the performance of an orthopedic implant. Thus, the objective of the present in vitro study was to compare the cytocompatibility properties of chemistries that may form at the Ti:HA interface, specifically HA, tricalcium phosphate (TCP), HA doped with Ti, and those containing calcium titanate (CaTiO3). In doing so, results of this study showed that osteoblast (bone-forming cells) adhesion increased with greater CaTiO3 substitutions in either HA or TCP. Specifically, osteoblast adhesion on HA and TCP composites with CaTiO3 was almost 4.5 times higher than that over pure HA. Material characterization studies revealed that enhanced osteoblast adhesion on these compacts may be due to increasing shrinkage in the unit lattice parameters and decreasing grain size. Although all CaTiO3 composites exhibited excellent osteoblast adhesion results, Ca9HPO4(PO4)(5) OH phase transformation into TCP/CaTiO3 increased osteoblast adhesion the most; because of these reasons, these materials should be further studied for orthopedic applications. (c) 2006 Wiley Periodicals, Inc.