We have previously described the purification and partial characterization of a serum glycopeptide with mucociliary activity from cystic fibrosis patients and a normal counterpart from sera of controls (3,4). After removal of its oligosaccharide component by β-elimination, the peptide portion of the glycopeptide from cystic fibrosis patients did not reveal any mucociliary activity on rabbit tracheal explants. This mucociliary activity was shown to be inhibited by mannose, glucose, and N-acetyl-galactosamine as well as by the glycopeptide purified from controls. It was not affected by xylose, fucose, galactose, or N-acetyl-glucosamine.