An injectable mixture for substituting bone tissue in situ comprises: A) a two-component powder/liquid bone cement which upon mixing forms a self-hardening cement paste; and B) a third component consisting of a liquid which essentially is non-miscible with the cement paste and which is suitable to be washed out after hardening of said mixture in situ, resulting in a porous bone substituting material; and C) an X-ray contrast agent which is an organic substance. The injectable bone substitute material for bone augmentation has adaptable mechanical properties, an optimal radio-opacity without any inorganic X-ray contrast agent and therefore good biocompatibility.