The 270 MHz Proton magnetic resonance spectra of N-epsilon-Me-His2-thyroliberin in solution in deuterium oxide and deuterated dimethylsulfoxide have been analyzed. All the spectral features (chemical shifts, coupling constants, temperature dependence of NH peptide resonances) clearly show that no significant conformational difference exists between thyroliberin and its analogue. Upon changing solvent from Me2SO-2H6 to 2H2O, both molecules undergo a conformational change which affects the carboxamide group and the backbone of the second residue.