A novel strategy is described for the preparation of dextran-protein conjugates containing disulfide linkages. "Dormant" protected thiol groups are introduced as side chains on dextran. These can, in a later stage, be converted into thiol-specific reactive disulfides by reaction with (alkoxycarbonyl)sulfenyl chloride. A dextran-protein conjugate is then easily formed by reaction with a thiol group of a cysteine side chain. The disulfide linkage between dextran and the model tripeptides reduced glutathione and N-Ac-L-Cys-L-Ala-L-Lys remains intact, even after 24 h of incubation at 37 degrees C in blood.