The peptide AcAla-Ser-Gln-Lys-Arg-Pro-Ser-Gln-Arg-His-Gly-Ser-Lys-Tyr, which comprises the first 14 residues of the acetylated N-terminus of myelin basic protein, is an epitopic site for two monoclonal antibodies to the human protein. The conformations of the tetradecapeptide in aqueous solutions were investigated employing high-resolution 1H- and 13C-NMR spectroscopy. Two-dimensional techniques were used to assign the spectra observed from both nuclei. Nuclear-Overhauser-effect data, amide proton temperature coefficients, 13C spin-lattice relaxation times, distance geometry calculations and dynamic simulated annealing provided evidence that the solution conformations of the tetradecapeptide included a nascent alpha-helix in the N-terminal segment, and a loop extending from Ser7 to Ser12 that bring His10 and Tyr14 into close proximity.