CO3apatites with different carbonate contents were synthesized at 60 +/- 1 degrees C and pH 7.4 +/- 0.2 under different carbonate concentrations (0-0.3 mol/L) in the supplied solutions. Their physicochemical properties were analyzed using various methods. Inductively coupled plasma gave accurate chemical analysis data for calcium and phosphate contents. X-ray diffraction analysis showed a clear chemical shift at high carbonate content. A CO3(2-) absorption peak area approximately proportional to carbonate content was observed through Fourier transmission infrared spectroscopy. Scanning electron microscopy and high-resolution transmission electron microscopy revealed a dramatic change of the crystal shape. Osteoblast proliferation at the surface of each CO3apatite-collagen sponge indicated that osteoblasts deformed to expand and cover the surface of the sponge, and appeared to adhere well to the sponge.