The purpose of our study was to test the effectiveness of Ostim nanocrystalline hydroxyapatite paste and Cerabone ceramic by treating a critical size bone defect (CSD) on the right foreleg of a white New Zealand rabbit. Evaluation was carried out by comparing four groups each with a different CSD filling: an only OSTIM bone filling, an only Cerabone filling, an OSTIM-Cerabone combination, and a control group with no filling of the CSD. The results of this study display a rapid and uniform bone ingrowth following the CSD filling with Ostim. The histological and histomorphometrical data have shown similarly excellent results for both the Ostim and Cerabone-Ostim groups. The control group faired poorly in comparison, as three cases of non-union were observed and none of the defects were totally refilled with fresh bone within 60 days. The successful bone healing with osseous consolidation verifies the importance of the nanocrystalline hydroxyapatite in the treatment of metaphyseal osseous volume defects in the metaphyseal spongiosa.