Chelidonium majus L. (Papaveraceae) has a long history as being useful for the treatment of many diseases in European countries. This plant is of great interest for its use also in Chinese herbal medicine. The plant contains, as major secondary metabolites, isoquinoline alkaloids, such as sanguinarine, chelidonine, chelerythrine, berberine and coptisine. Other compounds structurally unrelated to the alkaloids have been isolated from the aerial parts: several flavonoids and phenolic acids. C. majus extracts and its purified compounds exhibit interesting antiviral, antitumour and antimicrobial properties both in vitro and in vivo.