This invention is directed to the use of a chorionic gonadotrophin carboxy terminal peptide (CTP) or fragments thereof for modifying a polypeptide or a fragment thereof in order to increase the hydrodynamic volume of the polypeptide or fragment thereof. Biotechnology products cover an increased proportion of all therapeutic drugs, including monoclonal antibodies, vaccines, growth factors, hormones, cytokines, coagulation factors, fusion proteins, enzymes and other proteins.