Antioxidant systems of maize root cell walls grown on different nitrogen sources were evaluated. Plants were grown on a medium containing only NO 3 -or the mixture of NO 3 -+NH 4 + , in a 2:1 ratio. Eleven-day old plants, two days after the initiation of lateral roots, were used for the experiments. Cell walls were isolated from lateral roots and primary root segments, 2-7 cm from tip to base, representing zones of intense or decreased growth rates, respectively. Protein content and the activity of enzymes peroxidase, malate dehydrogenase and ascorbate oxidase ionically or covalently bound to the walls, as well as cell wall phenolic content and antioxidant capacity, were determined. Cell walls of plants grown on mixed N possess more developed enzymatic antioxidant systems and lower non-enzymatic antioxidant defenses than cell walls grown on NO 3 -. Irrespective of N treatment, the activities of all studied enzymes and protein content were higher in cell walls of lateral compared to primary roots. Phenolic content of cell walls isolated from lateral roots was higher in NO 3 --grown than in mixed N grown plants. No significant differences could be observed in the isozyme patterns of cell wall peroxidases isolated from plants grown on different nutrient solution. Our results indicate that different N treatments modify the antioxidant systems of root cell walls. Treatment with NO 3 -resulted in an increase of constitutive phenolic content, while the combination of NO 3 -+NH 4 + elevated the redox enzyme activities in root cell walls. Additional key words: nitrate; ammonia; antioxidant enzymes; phenolic compounds.