Using solution NMR spectroscopy, three-dimensional structures have been obtained for an 18-residue synthetic polypeptide fragment of kDa myelin basic protein (MBP, human residues Q81–T98) under three condi-tions emulating the protein’s natural environment in the myelin membrane to varying degrees: (a) an aqueous solution (100 mmKCl pH ), (b) a mixture of trifluoroethanol (TFE-d2) and water (30 : 70% v⁄v), and (c) a dispersion of 100 mm dodecylphosphocholine (DPC-d38 , 1 : 100 pro-tein⁄lipid molar ratio) micelles