1. Protein-polysaccharides isolated from bovine, human, and porcine cartilage are antigenic in the rabbit.
2. PP-L from each of these species contains a minimum of two antigenic determinants; one is species specific, and one is common to all three species. Human PP-H also contains these two determinants.
3. Both antigenic determinants are in, or closely associated with, the protein moiety of the compound. Chondroitin sulfate and keratan sulfate were not demonstrated to be antigenic in these studies.