Hydroxyapatite was prepd. by pptn. from an aq. soln. of CaO and H3PO4, dried by lyophilization at -53 degrees C for 72 h or under vacuum and studied for sp. surface, porosity and pore width. The product of lyophilization showed sp. surface 138.22 m(2)/g and under vacuum 120.38 m(2)/g. The ref. sample dried at 120 degrees C showed sp. surface 9,89 m(2)/g. The porosity was 83.28% 87.63% and 66.37%, resp.