A conjugate exhibiting interferon gamma activity and comprising at least one first non-polypeptide moiety covalently linked to an IFG polypeptide, the polypeptide comprising an amino acid sequence that differs from that of a parent IFNG polypeptide in at least one introduced and/or at least one removed amino acid residue comprising an attachment group for the non-polypeptide moiety. The conjugate may be used for treatment of various diseases.