Uniform distribution of cells and their extracellular matrix is essential for the in vivo success of bone tissue engineering constructs produced in vitro. In this study, the effects of biphasic calcium phosphate (BCP) granules embedded into chitosan scaffolds on the distribution, morphology, and phenotypic expression of osteoblastic cells were investigated. Mesenchymal stem cells (MSCs) and preosteoblasts were cultured on chitosan scaffolds with and without BCP under osteoblastic differentiation/ maturation conditions for periods up to 4 weeks. The addition of 25 wt % BCP to chitosan created a uniform layer of calcium phosphate (CaP) precipitation similar to bone mineral on the scaffold surfaces as determined by scanning electron microscopy and X-ray spectroscopy. Scaffolds with this CaP layer yielded more uniform and complete cell and ECM distribution than chitosan scaffolds without BCP. The suggestion of chemotaxis in the appearance of this response was confirmed by successive experiments in a Boyden chamber. The CaP layer also altered morphology of cells initially attached to the scaffold surfaces, leading to higher expression of marker proteins of osteoblastic phenotype including alkaline phosphatase and osteocalcin. The use of chitosan/BCP scaffolds for culture of MSCs and preosteoblasts enhances bone tissue development in vitro. (C) 2006 Wiley Periodicals, Inc. J Biomed Mater Res 81A: 624-633, 2007.