Model experiments using methyl α-d-galactopyranoside 6-sulfate have implied that the Carlson conditions (1 M sodium borohydride and 0.05 M sodium hydroxide at 45°C) for the release ofO-linked oligosaccharides from glycoproteins do not cause significant loss of sulfate ester groups. However the more vigorous conditions used to releaseN-linked oligosaccharides are more likely to cause considerable sulfate loss from a galactoside 6-sulfate as a result of 3,6-anhydride formation. Experiments with dextran sulfate suggested that sulfate loss due to oxirane formation was also not significant under the Carlson conditions. These results were supported by experiments with [35S]sulfate-labelled human rectal mucus glycoprotein.