(EN) A human granulocyte-colony stimulating polypeptide wherein at least one amino, carboxy, mercapto or guanidino group has been chemically modified by a chemical modifier; a platelet growth accelerator containing the polypeptide; a method of treating thrombocytopenic patients by administering an efficacious dose of the polypeptide; the use of the polypeptide for producing a pharmacological composition efficacious in treating thrombocytopenic patients; and a composition for treating thrombocytopenic patients comprising an efficacious dose of the polypeptide in a pharmacologically acceptable dosage form together with a pharmacologically acceptable carrier.