Elimination of the polymerization of glucagon has been achieved in the presence of glycols. The monomeric form of glucagon, found to be exclusively present under these conditions, is studied for its structural response to changes in the hydrophobicity of the environment. A reversible folding of the α-helix from about 0 to 80% is found to occur and it is suggested to proceed in two sequentially formed helical segments. Changes in the other spectroscopic properties are interpreted as changes in the tertiary structure. Implications for the biological activity are discussed.