The free acids, sodium salts, and lactones of several hexuronic acids have been studied as their O-trimethylsilyl derivatives by gas-liquid chromatography using SE-30 and XE-60 liquid phases. Silylation was best performed in methyl sulphoxide. The equilibrium between the various forms of a hexuronic acid in methyl sulphoxide was also studied by g.l.c. following silylation. The hexamethyldisilazane used in the silylation disturbed the equilibrium attained in the solvent, but this was overcome by premixing the hexamethyldisilazane with chlorotrimethylsilane. Methyl sulphoxide and the silylating reagents gave a two-phase system in which the derivative was favourably partitioned into the upper layer. Partition coefficients and stabilities of the derivatives were measured, and a g.l.c. method for the analysis of the hexuronic acids was thereby developed. The oximes of the hexuronic acids were studied as alternative derivatives for g.l.c., and their equilibrium compositions and g.l.c. retention times are recorded.