The objective of the present work was to evaluate the in vitro cellular response to hydroxyapatite (HA) scaffolds with oriented pore architectures. Hydroxyapatite scaffolds with approximately the same porosity (65-70%) but two different oriented microstructures, described as 'columnar' (pore diameter = 90-110 μm) and 'lamellar' (pore width = 20-30 μm), were prepared by unidirectional freezing of suspensions. The response of murine MLO-A5 cells, an osteogenic cell line, to these scaffolds was evaluated using assays of MTT hydrolysis, alkaline phosphatase (ALP) activity, and alizarin red staining. While the cellular response to both groups of scaffolds was better than control wells, the columnar scaffolds with the larger pore width provided the most favorable substrate for cell proliferation and function. These results indicate that HA scaffolds with the columnar microstructure could be used for bone repair applications in vivo.