In this study, the specific objective was to investigate the combined effect of different treatments of transforming growth factor-ß (TGF-ß) and hydroxyapatite (HA) on osteoblast response in vitro. Since the nature of bone cell responses in vitro is influenced by the properties of HA ceramics, this study was divided into 2 components: a chemical and crystallographic characterization of the HA ceramics, and an in vitro cell culture study. Sintered HA samples were observed to have the highest crystallite size, compared to as-received HA and calcined HA samples. No differences in surface roughness and chemical composition were observed between the sintered, calcined, and as-received HA surfaces. In concurrence with the x-ray diffraction, high-resolution x-ray photoelectron spectroscopy of Ca 2p also indicated a higher crystallinity on sintered HA samples compared to calcined and as-received HA samples. Protein production by osteoblast cells was not statistically different on the 3 HA surfaces in the absence of TGF-ß. However, there was a dose-dependent increase in TGF-ß-stimulated protein production on the 3 different HA surfaces. As indicated by increased alkaline phosphatase-specific activity, as well as 1,25 (OH2) vitamin D3-stimulated osteocalcin production, a more differentiated osteoblastlike phenotype was observed on the sintered HA surfaces compared to the as-received HA and calcined HA surfaces. An increased osteoblast-like cell activity on sintered HA surfaces in the presence of different TGF-ß dosage suggested that sintering of HA surfaces may play an important role in governing cellular response. Schlagwörter: alkaline phosphatase activity, heat treatments, hydroxyapatite, osteocalcin concentration, transforming growth factor-ß