Disclosed is a method for refolding a protein or peptide that does not contain essential disulfides and that contains at least one free cysteine residue. Also disclosed are polymer IFN-.gamma. conjugates that have been created by the chemical coupling of polymers such as polyethylene glycol moieties to IFN-.gamma., particularly via a free cysteine in the protein. Also disclosed are analogs of bioactive peptides that may be used to create longer acting versions of the peptides, including analogs of glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, Gastric inhibitory peptide (GIP), PYY, exendin, ghrelin, gastrin, amylin, and oxyntomodulin.