The environment of carbonate ions in bones of different species (rat, rabbit, chicken, cow, human) was investigated by Fourier Transform Infrared Spectroscopy (FTIR) associated with a self-deconvolution technique. The carbonate bands in the ν₂ CO₃²⁻ domain show three components which were identified by using synthetic standards and different properties of the apatitic structure (ionic affinity for crystallographic locations, ionic exchange). The major component at 871 cm⁻¹ is due to carbonate ions located in PO₄³⁻ sites (type B carbonate). A band at 878 cm⁻¹ was exclusively assigned to carbonate ions substituting for OH− ions in the apatitic structure (type A carbonate). A band at 866 cm⁻¹ not previously observed was shown to correspond to a labile carbonate environment. The intensity ratio of type A to type B carbonate appears remarkably constant in all bone samples. The 866 cm⁻¹ carbonate band varies in its relative intensity in different species.