Here, we prove that dehydroleucodine, a sesquiterpene lactone, at low concentrations (25-100 microM) slowed down the Allium cepa L root growth by 22-70% respectively neither affecting cell viability nor cell size. Removal of the drug after 24 h incubation restored the normal growth rate of the roots. Higher concentrations (200 microM) of dehydroleucodine were deleterious for the roots. As cell size did not change, it is most likely that dehydroleucodine affected some event of cell division cycle making it longer. Thus, dehydroleucodine could be a useful tool to slow down cell proliferation.