Flame-spray synthesis was used to produce nanoparticulate X-ray amorphous tricalcium phosphate. Upon heating, the material crystallized at temperatures between 525 degrees and 600 degrees C, yielding alpha-tricalcium phosphate (TCP) with minor amounts of beta-TCP and hydroxyapatite (HA). Further heating induced a gradual transformation of alpha- to beta-TCP accompanied by crystallite growth and particle fusion. alpha-TCP was completely transformed into beta-TCP at 950 degrees C. The high-temperature polymorph alpha'-TCP was not observed. In transmission electron microscopy and selected area electron diffraction analyses, the raw material appeared completely amorphous and samples heated previously to 600 degrees and 700 degrees C comprised single-crystalline particles of alpha-, beta-TCP, and HA. The results of this study demonstrate that nanoparticulate alpha-TCP can be obtained from flame-spray-synthesized amorphous nanoparticles at temperatures where sintering effects such as particle growth and fusion are moderate, if not negligible.