The introduction of sulphate groups into dextran produces characteristic changes in its proton magnetic resonance spectrum. With linear dextran a new signal appears which can be attributed solely to an effect of sulphate groups; with branched dextran this signal coincides with that due to the branching. From a comparison of peak areas in these spectra with peak areas in the spectra of the unsulphated linear and branched dextrans it is concluded that during sulphation no appreciable degradation occurred, whether by chain scission or branch hydrolysis.The proton magnetic resonance spectra also provide evidence for preferential substitution of sulphate at carbon 2 in the anhydroglucose unit.