The kinetics of spontaneous precipitation of vaterite (CaCO3) from an aqueous solution in the presence of chondroitin sulfates (CSA, CSB, CSC) was investigated by the constant composition method. The presence of chondroitin sulfate in the supersaturated solution resulted in a reduction of the crystal growth rate by 23-65%. Induction times preceding vaterite precipitation were inversely proportional to the solution's supersaturation and a surface energy of 52 mJ m(-2) was calculated according to the classical nucleation theory. Chondroitin sulfate influences the particle size distribution of the vaterite crystals formed and stabilizing this mineral phase, preventing the transformation to calcite. The apparent order found from kinetics data was n > 2, thus suggesting a surface nucleation mechanism.