With typical molecular weights of 500 ～20000, polyethylene glycol (PEG) is nontoxic, nonimmunogenic and soluble in aqueous solutions as well as in most organic solvents. The covalent attachment of PEG (pegylation) to peptides and proteins can significantly improve their pharmacological and biological properties, such as shielding immunogenic epitopes, preventing degradation by proteolytic enzymes, increasing solubility, reducing renal filtration and altering biodistribution. Some methods in this field especially on site- directed pegylation for amino, carboxyl and thiol groups of peptides and proteins are reviewed.

Key words: POLYGLYCOL;CHEMICLAL MODIFICATION;POLYPEPTIDE;PROTEIN, PHARMACOKINETICS