Three types of biomaterials based on hydroxyapatite are synthesized and investigated. Hydroxyapatite nanocrystals or microcrystals precipitated from low-temperature aqueous solutions serve as the initial material used for preparing spherical porous granules approximately 300-500 mu m in diameter. Sintering of hydroxyapatite crystals at a temperature of 870 degrees C for 2 h or at 1000 degrees C (for 3 h) + 1200 degrees C (for 2 h) brings about the formation of solid ceramics with different internal structures. According to the electron microscopic data, the ceramic material prepared at 870 degrees C is formed by agglomerated hydroxyapatite nanocrystals, whereas the ceramics sintered at 1200 degrees C (with a bending strength of the order of 100 MPa) are composed of crystal blocks as large as 2 mu m. It is established that all the biomaterials have a single-phase composition and consist of the hydroxyapatite with a structure retained up to a temperature of 1200 degrees C.