A simple assay for O-glycosylated glycoproteins involving the liberation of oligosaccharides by beta-elimination with dilute alkali and the subsequent derivatization of the reducing end with 2-cyanoacetamide is reported. The method can be used to quantitate microgram amounts of mucin within 30 min. The assay is 30 times less sensitive to protein or N-linked glycoproteins and 100 times less sensitive to DNA than to the corresponding weight of canine tracheal mucin. Of the substances tested, only cesium chloride and potassium thiocyanate caused substantial interference, but in neither case was this sufficiently serious to prevent the method being used for monitoring mucin purification schemes utilizing these reagents. The coefficients of variation for replicate analyses of canine tracheal mucin (14.0, 5.0, and 2.0 micrograms) were 3.6, 6.5, and 12.3%, respectively.