Competitive and cooperative adsorptions of bovine serum albumin (BSA) and lysozyme (LSZ) on synthetic calcium hydroxyapatite (CaHap) were investigated at 15 degrees C in deionized distilled water of pH 6 by using a liquid chromatography method. The adsorption rate of LSZ was faster than that of BSA due to its larger diffusion coefficient, though the saturated adsorption amount of LSZ was less than that of BSA. The rates of BSA adsorption onto CaHap did not change by the addition of LSZ, while those of LSZ were considerably reduced by addition of BSA with forming (BSA(-)-LSZ(+)) agglomerates in the solution. The cooperative adsorption behavior of LSZ was observed in the presence of lower amounts of BSA due to the preferential adsorption of the larger (BSA(-)-LSZ(+)) agglomerates. However, in the case of higher BSA content, the adsorption of LSZ was inhibited by capturing the LSZ molecules in the (BSA(-)-LSZ(+)) agglomerates. The similar cooperative adsorption behavior of BSA was also observed on all systems examined in the presence of various amounts of LSZ.