The present invention provides polypeptides that include an O-linked glycoconjugate in which a species such as a water-soluble polymer, a therapeutic agent of a biomolecule is covalently linked through an intact O-linked glycosyl residue to the polypeptide. The polypeptides of the invention include wild-type peptides and mutant peptides that include an O-linked glycosylation site that is not present in the wild-type peptide. Also provided are methods of making the peptides of the invention and methods, pharmaceutical compositions containing the peptides and methods of treating, ameliorating or preventing diseased in mammals by administering an amount of a peptide of the invention sufficient to achieve the desired response.