All the five hexuronic acids that are known to occur naturally have been synthesised in the form of their methyl α- and β-glycosides, to provide model compounds with which to assess the scope of circular dichroism for the analysis of these residues in biological materials. In the acid form the sign of the c.d. is found to be dictated by configuration at C(5). C(4) Configuration determines the presence or absence of an anomalous long-wavelength band which is opposite in sign to the main n→π* band, and has previously been reported as a minor feature in the spectra of many acyclic α-hydroxy- and α-amino-carboxylic acids. For uronic acid derivatives with O(4) equatorial this band is comparable in size to the normal n→π* band, but it is totally absent when O(4) is axial. These generalisations also apply to spectra of the salts, although band form and position are very different. These variations of c.d. with structure and conformation may be used for the analysis of polysaccharides which contain uronic acid residues. The alginates, which are linear copolymers of L-guluronate and D-mannuronate residues, provide a particularly favourable example.