A new modification of pulsed-ionization high-pressure mass spectrometry (PHPMS) has been used to perform equilibrium thermochemical studies for relatively nonvolatile biomolecules such as amino acids. Binding enthalpy and entropy changes have been measured for proton-bound clusters of glycine, which are in good agreement with both theoretical (DFT) results of this work and a previous blackbody infrared dissociation experiment. Experimental data indicate that a number of conformers of the proton-bound dimer of glycine may coexist in the explored temperature range (360–460 K). Several new, conceptually different isomers (two of them zwitterionic) have been found by DFT calculations, one of which is 7 kJ mol−1 lower in energy than the structure previously reported to be the energy minimum. Copyright © 2005 John Wiley & Sons, Ltd.