CONFORMATIONAL analysis of peptides in solution by nuclear magnetic resonance (NMR) spectroscopy generally involves determination of the relative exposure to solvent of specific NH hydrogens1-4. The four methods used so far are based on: (1) rates of NH proton exchange with labile hydrogens of the solvent5-6; (2) temperature dependence of chemical shifts of NH resonances7-8; (3) dependence of NH chemical shifts on the composition of a suitable solvent mixture3,9-11, and (4) degree of resonance broadening when a paramagnetic substance is added12. Each method has limitations. Proton exchange rates reflect not only exposure to solvent, but also proximity to functional groups of the peptide which catalyse exchange. Factors which determine the temperature dependence of NH chemical shifts are as yet poorly understood. Changes in solvent composition can alter the conformation of the peptide11. Paramagnetic ions may associate preferentially with the solvent or with specific sites on the peptide.