Decorin, a small proteoglycan containing a dermatan sulfate (DS) chain, is expressed abnormally in human colon cancer stroma. The aim of this study was to determine neoplastic changes in DS chains from human colon cancer and normal colonic mucosa. Proteoglycans were extracted from human colon cancer and normal colonic mucosa and successively digested with enzymes. The glycosaminoglycan obtained was fluoro-labeled with 2-aminopyridine at reducing terminals and fractionated by HPLC. Fluoro-labeled DS chains were collected and digested with bovine testicular hyaluronidase, followed by HPLC. The repeating disaccharide connected to the linkage region [glucuronosyl-galactosyl-galactosyl-xylosyl(2-aminopyridine)] of pyridylaminated DS chains from both types of tissue was glucuronosyl-N-acetylgalactosamine. The other glucuronic acid of the pyridylaminated DS chain was located 12 saccharides from the reducing terminal in colon cancer, and 18 saccharides from the reducing terminal in normal colon. The saccharide sequence of DS chains from human colon cancer is altered from that in normal colon.