A polyheptapeptide poly (Ala‐Leu‐Lys‐Glu‐Ala2‐Glu) has been synthesized by polymerization of the blocked heptamer and by sequential synthesis. The former method yields molecular weights up to 40, 000, the latter a product of rather uniform D.P = 25, i.e. a molecular weight Mr= 18, 250. The polypeptide was designed to have a repeat sequence of hydrophobic residues of the type expected in α‐keratin and in tropomyosin and was designed to optimize hydrophobic bonding between two chains.Preliminary characterization indicates that in aqueous solution the polypeptides are random at all pH, but high molecular weight material shows a small amount (up to 20%) of α‐helix. However, crystallization of the material from certain solvents and solvent mixtures including chloroform I trifluoroacetic acid and hexafluoroisopropanol, produces α‐helical material which in some cases is crystalline.Electron microscopy of the crystalline material shows lozenge‐shaped crystals of about 1 μ in maximum side and ˜ 300 Å thick. Diffuse electron diffraction has been obtained with d = 16.1 Å. The hexafluoroisopropanol‐precipitated material, which is α‐helical by infrared spectroscopy and film circular dichroism, gives a diffuse X‐ray diffraction pattern with d = 5.1 å and d = 2.5 å. Attempts to orient the material caused distortion toβ‐sheet form. The diffraction studies are consistent with an α‐helix coiled coil and a tentative cell packing arrangement is described.