As a continuation of our work on Argentinian plants toxic to cattle, we report here for the first time the flavonoids, terpenoids, steroids, and pyrrolizidine alkaloids of Senecio vira-vira Hieron. (Compositae; tribe Senecioneae). As far as we know, this is the first report on the Occurrence of isorhamnetin 3-O-β-robinobioside in the Compositae. It has been previously found in the Amaranthaceae (1). Uspallatine has been isolated only from Senecio mallatensis (2).