Two novel compounds, 8-C-D-glucopyranosyl-7-hydroxy-5-methylchromone-2-carboxylic acid and a 2-O′-p-coumaroyl derivative thereof, were identified in a herbal tea that caused severe vomiting in a South African patient who had taken the traditional remedy to clean his stomach. For structural characterization, electrospray (ES) ionization in combination with collision-induced dissociation (CID) and tandem mass spectrometry (MS/MS) were used, as well as UV and nuclear magnetic resonance (NMR) spectroscopy. Specific ions or neutral losses generated under conditions of ES-MS/CID/MS permitted the establishment of structural features such as the free carboxyl group, the C-hexosidic part and the p-coumaroyl group. NMR spectroscopy was necessary to support the structure of the chromone-type aglycone and the glucosidic parts. Since the compounds are structurally related to aloesin and aloeresin A, which are chemotaxonomic markers of Aloe species, and have not been previously reported, we propose that they were formed by oxidative degradation during preparation of the herbal tea from an Aloe species or during its storage. Copyright © 2002 John Wiley & Sons, Ltd.