1) A new method of enrichment of the linkage-region in corneal proteokeratan sulfate is described, which consists of desulfation of peptidokeratan sulfate, followed by chromatography on Con A-Sepharose 4B and enzymatic degradation with beta-D galactosidase and beta-N-acetyl-D-glucosaminidase. 2) After permethylation, hydrolysis, reduction with sodium borohydrid and acetylation gas chromatography/mass spectrometry analyses were performed. The followings products could be detected as their peracetates: 2,3,4-tri-O-methylfucitol; 2,3,4,6-tetra-O-methylmannitol; 3,4,6-tri-O-methylmannitol; 2,4-di-O-methylmannitol; 2,3,4,6-tetra-O-methylgalactitol; 2,4,6-tri-O-methylgalactitol; 2,4-di-O-methylgalactitol. 3) The results point to the presence of a branched linkage region in the proteokeratan sulfate molecule with one mannose as the branching point and two mannose residues as the starting point of two disaccharide chains.