A particularly numerous and widespread category of vegetable matter with carcinogenic effect are pyrrolizidine alkaloids. They are present in hundreds of plants, especially in the different varieties of Senecio, but also in those of crotalaria, Heliotropium, Lappul, Symphytum, Petasites and Tussilago farfara. A large number of these plants can be found in herbalist stores since they have a therapeutic use; they may contaminate cereals used for human consumption, and honey; and they are used in the preparation of certain beverages or even as foodstuffs. Extracts of Tussilago farfara are even ingredients in certain shampoos and skin cleansers. Among the different pyrrolizidinic alkaloids which have been identified, the most well known are senkirkine, hydroxysenkirkine, senephicilline, isatidine, jacobine, lasiocarpine, monocrotaline, retrorsine, riddelline, petasitenine and symphitine., In general, they are mutagenic, teratogenic and hepatotoxic, with the latter having also been highlighted in man. In the rat, apart from certain pure alkaloids, only the products of plants which contain them have proved to be carcinogenic, especially for the liver where they are transformed into pyrrole reactive metabolites.