Two new 13-membered macrocyclic pyrrolizidine alkaloids, (13R)-13-hydroxyretroisosenine (2b) and (12S)-12-hydroxyretroisosenine (2c), have been isolated from Senecio roseus and Senecio helodes. Their structures were established from spectral and chemical studies including 2D NMR. The hydrochloride of retroisosenine (2a'HCl) was also isolated, and its absolute configuration was determined by X-ray diffraction analysis.