In a preliminary communication last year(1) we stated that there are only two helical configurations of polypeptide chains in which the residues are all equivalent and intramolecular hydrogen bonds are formed, and in which the interatomic distances, bond angles, and other structural features, especially the coplanarity of the conjugated amide system, are as required by earlier work in these Laboratories on amino acids, simple peptides, and other substances related to protein's. These two helical configurations were described in detail in a later paper(2) and it was mentioned that there is evidence that they occur in α keratin, α myosin, supercontracted keratin and myosin, and other fibrous proteins, and also constitute an important structural feature of hemoglobin and other globular proteins.(3) In the following paragraphs we discuss evidence that one of the helical structures is assumed also by synthetic polypeptides.