The monosaccharide contents of solid lignosulphonate products from spent sulphite liquors were determined by capillary gas chromatography. The predominant monosaccharide was mannose in two softwood calcium bisulphite cases, and xylose in a hardwood calcium bisulphite case. Monosaccharide analysis before and after ultrafiltration of lignosulphonates showed that about 10–25% of the neutral sugars did not pass through the membranes, and presumably remained associated with the lignosulphonates. Chemical “de-sugaring” treatments removed all but traces of the monosaccharides; when hot aqueous sodium hydroxide was used for this purpose, the main products were 3-deoxy carboxylic acids derived from the hexoses.