The formation of hydroxyapatite (HA) from a sol-gel precursor was studied using X-ray diffraction (XRD). The sol-gel was processed into both powders and thin films. The effect of drying and firing temperatures on the HA phase formation was studied. Thin HA films up to 1 mu m thick were deposited on silicon wafers coated either with borophosphate silicate glass (BPSG) or titanium films, dried and then fired. Increasing the drying temperature raised the firing temperature for initial formation of crystalline HA. It was found that at firing temperatures ranging from 300 to 1000 degrees C, the dominant phase in the powders was HA with small amounts of calcium oxide and beta-tricalcium phosphate (beta-TCP). As the firing temperature increased the amount of CaO and beta-TCP increased. At firing temperatures ranging from 300 to 500 degrees C the only observable crystalline phase in the films was HA.