A statistical mechanical treatment concerning the helix-helix transition of polypeptide chains was attempted based on a model which specifies the state of each peptide residue by either right-handed screw sense or left-handed screw sense.Two principal parameters were introduced. γ is the statistical weight of a right-handed helical residue that follows one or more other right-handed helical residues ρ represents the difficulty for the initiation of a right-handed sequence after a run of left-handed segments

To account for the newly discovered multiple helix-helix transitions

the acid effect was further incorporated into the theory.The proposed theory was compared with experimental results and some published data

and the agreement is encouraging.