Previous work by the authors showed that hydroxyapatite (HA) scaffolds with different types of oriented microstructures and a unique 'elastic-plastic' mechanical response could be prepared by unidirectional freezing of suspensions. The objective of the present work was to evaluate the in vitro cellular response to these freezecast HA scaffolds. Unidirectional scaffolds with approximately the same porosity (65-70%) but different pore architectures, described as 'lamellar' (pore width = 25 ± 5 lm) and 'cellular' (pore diameter = 100 ± 10 lm), were evaluated. Whereas both groups of scaffolds showed excellent ability to support the proliferation of MC3T3-E1 pre-osteoblastic cells on their surfaces, scaffolds with the cellular-type microstructure showed far better ability to support cell proliferation into the pores and cell function. These results indicate that freeze-cast HA scaffolds with the cellular-type microstructure have better potential for bone repair applications.