Dextrans partially modified with cyanoethyl groups were obtained by reaction of dextran with acrylonitrile in alkaline medium. The structure of the resulting polymers was determined by means of infra-red spectroscopy and H-1 and C-13 nuclear magnetic resonance (n.m.r.) spectroscopy. The influence of solvent composition, temperature and acrylonitrile concentration as well as the type and concentration of catalyst was evaluated. C-13 n.m.r. spectra at 75.4 MHz of partially modified dextran with cyanoethyl groups were studied in order to evaluate the selectivity of the reaction of dextran with acrylonitrile in the homogeneous phase. Analysis of the spectra of ring carbons in the anhydroglucose units shows that the reactivity of the individual hydroxyl groups decreases in the order C2 > C4 > C3. Nitrile groups in cyanoethylated dextran were converted to amidoxime groups by reaction with hydroxylamine. The activation energy was found to be 42.7 kJ mol(-1). Preliminary experiments showed the Cu2+ complex formation ability of amidoximated dextran.