3-D ordered macroporous sol-gel bioactive glass particles (3DOM-BG, pore size: 345 nm; molar composition: 75 SiO2-21 CaO-4 P2O5) were converted into nano-crystalline calcium-deficient carbonate apatite after soaking at 37 degrees C in simulated body fluid. The as-formed, flake-like apatite transformed into a coral-like, highly crystalline hydroxyapatite with a minor tricalcium phosphate phase after heating for I h at a temperature of 700 degrees C. Fourier transform infrared results show the loss of carbonate and isolation of hydroxyl during heating. The heat treatment improved the apatite's resistance to dissolution in a buffer solution (pH = 5).