The present study aimed at investigating effects of zinc and aluminum (0.15 and 0.3mM) in duckweed (Lemna minor L.) over a 15-day period. High bioaccumulation of both metals was accompanied by an increase in dry weight under higher metal treatments. Antioxidant response was observed under both metal stresses, with large increases in superoxide dismutase and peroxidases. Catalase activity declined only in duckweed exposed to Zn while lipid peroxidation as well as H(2)O(2), proline and ascorbate levels increased. The results suggest induction of oxidative stress under both aluminum and zinc toxicity, and also demonstrate duckweed's capacity to upregulate its antioxidative defense. Additionally, Zn was found to be more toxic than Al to duckweed for the concentrations applied. Due to its high bioaccumulation potential and tolerance via increased antioxidant capacity, duckweed has a potential for phytoremediation of water bodies polluted by low levels of zinc and aluminum.