Platelet proteo-chondroitin sulfates localize on the surface and in the granules. Western blotting method is able to selectively detect core-proteins prepared from proteo-chondroitin sulfates by chondroitinase ABC digestion. A very highly sensitive high-performance liquid chromatographic method was established for the determination of chondroitin sulfates as their unsaturated disaccharides. These methods were applied to rabbit platelet proteo-chondroitin sulfates. It was found that both rabbit platelet surface proteo-chondroitin sulfate and granule proteo-chondroitin sulfate consist of a predominantly homogeneous chondroitin 4-sulfate and a single core-protein having a molecular weight of approximately 26 kDa.