Biomedical materials and, in particular, to substituted calcium phosphate (e.g. apatite and hydroxyapatite) materials for use as synthetic bone. A synthetic calcium phosphate comprising silicon and a trivalent cation having a formula Ca.sub.10-yM.sub.y(PO.sub.4).sub.6-x(SiO.sub.4).sub.x(OH).sub.2-x+y where M is a trivalent cation, 0