The aim of this work was to determine the compartmentation of antioxidants between the bundle-sheath and mesophyll cells of maize (Zea mays L.) leaves. Rapid fractionation of the mesophyll compartment was used t o minimize modifications i n the antioxidant status and composition due to extraction procedures. The purity of the mesophyll isolates was assessed via the distribution of enzyme and metabolite markers. Ribulose-1,Ei bisphosphate and ribulose-1,5-bisphosphate carboxylase/oxygenase were used as bundlesheath markers and phosphoenolpyruvate carboxylase was used as the mesophyll marker enzyme. Clutathione reductase and dehydroascorbate reductase were almost exclusively localized i n the mesophyll tissue, whereas ascorbate, ascorbate peroxidase, and superoxide dismutase were largely absent from the mesophyll fraction. Catalase, reduced glutathione, and monodehydroascorbate reductase were found to be approximately equally distributed between the two cell types. It is interesting that, whereas H,O, levels were relatively high in maize leaves, this oxidant was largely restricted to the mesophyll compartment. We conclude that the antioxidants in maize leaves are partitioned between the two cell types according to the availability of reducing power and NADPH and that oxidized glutathione and dehydroascorbate produced in the bundle-sheath tissues have to be transported to the mesophyll for re-reduction to their reduced forms.