A convenient route of obtaining recombinant human proinsulin from the hybrid protein produced by the bacteria was developed. Chimeric protein was prepared by ultra- or gel-filtration, immobilized on thiol-support at cysteine residues and cleaved by cyanogen bromide to liberate purified proinsulin. Conditions of treatment hybrid protein with cyanogen bromide at methionine residues without affecting disulfide bonds between proinsulin and support are described. Proinsulin with correct disulfide bonds, directly obtained from polymer--attached polypeptide, followed was converted into insulin.