An N a -protected model pentapeptide containing two consecutive DPhe residues, Boc-Leu-DPhe-DPhe-Ala-Phe-NHMe, has been synthesized by solution methods and fully characterized. 1 H-nmr studies provided evidence for the occurrence of a significant population of a conformer having three consecutive, intramolecularly H-bonded b-bends in solution. The solid state structure has been determined by x-ray diffraction methods. The crystals grown from aqueous methanol are orthorhombic, space group P2 1 2 1 2 1 , a Å 11.503(2), b Å 16.554(2), c Å 22.107(3) A ˚, V Å 4209(1) A ˚,3 and Z Å 4. The x-ray data were collected on a CAD4 diffractometer using CuK a radiation (l Å 1.5418 A ˚). The structure was determined using direct methods and refined by full-matrix least-squares procedure. The R factor is 5.3%. The molecule is characterized by a right handed 3 10 -helical conformation (»f… Å 068.2Њ, »c… Å 026.3Њ) , which is made up of two consecutive type III b-bends and one type I b-bend. In the solid state the helical molecules are aligned head-to-tail, thus forming long rod like structures. A comparison with other peptide structures containing consecutive DPhe residues is also provided. The present study confirms that the -DPhe-DPhe-sequence can be accommodated in helical structures.