The structure of the repeat region and chain caps of the N-linked keratan sulphate chains attached to bovine tracheal cartilage fibromodulin has been examined. The chains were fragmented by keratanase digestion, the resultant oligosaccharides isolated by strong anion-exchange chromatography, and their structures determined using high-field 1H-n.m.r. spectroscopy. The chains were found to possess the following general structure: [formula: see text] All of the capping oligosaccharides isolated terminate with alpha(2-3)-linked N-acetylneuraminic acid. No alpha(2-6)-linked N-acetylneuraminic acid chain terminators, nor any fucose, alpha (1-3)-linked to N-acetylglucosamine along the repeat region, were detected. This work demonstrates that the structure of the repeat region and chain caps of N-linked keratan sulphate attached to fibromodulin isolated from bovine tracheal cartilage is identical with that of O-linked keratan sulphate chains attached to aggrecan derived from non-articular cartilage.