The infusion of the semi-fresh flowering aerial parts of Sisymbrium officinale (L.) Scop. (Brassicaceae), commonly known as hierba del canto in Spanish, is a popular remedy for the treatment of sore throats, coughs, and hoarseness, but little is known about its chemistry and pharmacology. HPLC-UV/PDA analyses of the dichloromethane and methanol extracts of both the fresh and the dried plant material showed the occurrence of some biochemical reactions during the drying process. The freeze-dried residue of the infusion (SOw) prepared according to the traditional recipe, was re-dissolved in methanol obtaining a soluble fraction (SOw_s) and a precipitate (SOw_p). Further fractionation of SOw_s allowed the identification of adenine, adenosine, and guanosine that were present in significant quantities only in the traditionally prepared aqueous extract. Polysaccharides were detected in the SOw_p fraction and their molecular weight evaluated by DOSY experiments. When they all were tested for the topical anti-inflammatory activity in the murine Croton oil-induced ear oedema model, only a modest effect was observed at high concentrations. Saturation Transfer Difference-NMR experiments for the study of the binding activity between the plant metabolites and the Lens culinaris lectin gave partial data on the active principles. This work affords new data on the phytochemistry of the plant but the question about the identity of the active principles responsible for the traditional use of S. officinale remains open. © 2008 Los Autores.