The present in vitro study investigated osteoblast adhesion on hydroxylapatite (HA) doped with either cadmium (Cd), zinc (Zn), magnesium (Mg), or yttrium (Y). Compared with any other dopant tested in the present study, osteoblast adhesion was significantly (p < 0.05) greater on HA doped with Y after 4 h; in addition, osteoblast adhesion increased with concentration (2-7 mol%) of Y in HA. The findings that HA doped with greater amounts of Y adsorbed higher concentrations of calcium and, subsequently, of vitronectin and collagen (proteins known to mediate osteoblast adhesion), but not of albumin, laminin, and fibronectin, may explain the observed enhanced adhesion of osteoblasts on these substrates. Interactions (i.e., adsorption and configuration/bioactivity) of vitronectin and collagen may have been promoted by increased porosity of doped HA. Through doping with Y, the present study provided the first evidence that HA can be synthesized and processed with improved cytocompatibility properties for osteoblast adhesion, and thus offered essential information for the design of novel proactive bioceramics. Proactive bioceramics which elicit specific, timely, and desired responses from surrounding cells and tissues are necessary for improving bonding of orthopaedic/dental implants to juxtaposed bone; such osseointegration will, undoubtedly, enhance implant efficacy. (C) 2001 John Wiley & Sons, Inc.