Mass spectrometry has been usefully employed in the study of the products arising from in vitro and in vivo glycation of proteins. In particular, daughter-ion spectroscopy has led to an easy detection of 2-(2-furoyl)4-(5)2(furanyl)1-H-imidazole in HCl-hydrolysed glycated albumen and polylysine and the method has allowed us to exclude the presence of the same molecule in in vivo glycated proteins. Parent-ion spectroscopy has been successfully employed in the identification of furoyl-containing compounds, which are possibly responsible for the results obtained with other analytical approaches.