The Enemy Release Hypothesis predicts that exotic plants gain an advantage over native competitors by losing their natural enemies while invading new regions. However, this assumes that those enemies reduced the performance of these invaders in their native ranges, and this may not be true if an invader is highly tolerant of herbivory. We used a field experiment to test the herbivore tolerance of a North American annual, common ragweed (Ambrosia artemisiifolia L.), which is known to have lost insect herbivores while invading Europe. We clipped leaves to simulate damage by folivores and removed meristems to simulate apical mortality caused by stem borers, and measured the consequences for growth and reproduction. Stem biomass was only reduced by defoliation far in excess of native-range natural damage, while seed production was unaffected by our treatments. Severely damaged plants maintained seed production by allocating relatively more aboveground biomass to reproduction. These results suggest that for the most part, damage by natural enemies may have little impact on this highly tolerant plant; consequently, enemy release may not have provided a significant advantage to this species in Europe. As well, biological control by insect folivores is unlikely to succeed unless it results in very high levels of damage.