The role of carbonate on the kinetics and physicochemical characteristics of the crystal growth of stoichiometric hydroxyapatite was investigated at 37 degrees C, 0.15 M NaCl ionic strength, and pH 7.40 at constant supersaturation. It was found that at low supersaturations the presence of carbonate ions at concentration as high as 0.1 mM had no effect on the crystal growth kinetics while at higher supersaturation (>3.8) the presence of carbonate ions resulted in reduction of the crystal growth rates and changed the dependence of the rates of crystal growth on the solution supersaturation from parabolic to linear. Carbonate was incorporated to the apatite growing on the seed crystals and caused changes in their morphology, favoring platelike formations.