Structural analysis of gallotannins is currently carried out in the following steps: - extraction from the natural Matrix; -chromatographic isolation/putrification; - chemical or enzymatic hydrolysis of the tannins; - instrumental/chemical analysis of the hydrolytic products. The present investigation with the model compound the gallotannin Hamamelitannin, has dealt with the following: 1) choice of the best mass spectrometric technique for direct structural identiifcation of this molecule, isolation from Hamamelis virginiana L. bark, without any chemical manipulation: direct electron impact (DEI), direct chemical ionization (DCI), field desorption (FD) and positive and negative fast atom bombardment (FAB): 2) establishment of a mass spectrometric approach (MS/MS and FAB-MS) for the direct identification of this gallotannin species in the natural matrix, to minimize or eliminate all the extraction and chromatography steps to obtain quickly the unequivocal structure of the molecule.