Substantially pure histidine-linked protein-polymer conjugates and processesfor their preparation are disclosed. The processes include contacting aprotein with an activated polymer under conditions sufficient to facilitatecovalent attachment of at least a portion of the polymer strands on histidineresidues of the protein and thereafter substantially separating the histidine-linked conjugates from the remaining reactants. Linkage through His-34 ofalpha interferon is exemplified.
