Bioceramics based on silicon stabilized tricalcium phosphate [Si-TCP] have been investigated by attenuated total reflection infrared spectroscopy using an experimental preparation that ensures consistent high-quality spectral data. Phase normalized measurements show that changes in OH bands are primarily due to a decrease in the hydroxyapatite content; however, a band at 945 cm(-1) associated with dehydration of the apatite is visible and correlated with silicon doping. Changes in absorption bands with Si content associated with PO43- differ for SiO2 doping levels less than and greater than 0.2 mol Of SiO2/mol of HA as the amount of Si-TCP phase saturates. Increased resolution allows the study of weak bands linked to Si at 668, 800, 863, and 892 cm(-1) and suggests that the loss Of PO43- coincides with the development of different silicate groups-SiO4 at lower doping levels and a new silicon species at higher doping.