Glutathione and ascorbate are considered the major redox buffers in plant cells. They are implicated in many reactions at the sub-cellular level. However, information about the location and quantification of glutathione in the different sub-cellular compartments is very scarce and it has been obtained mainly using organelle purification and chemical quantification. We have used a glutathione antibody to immunolabel and quantify the total glutathione in leaves from wild-type Arabidopsis thaliana (Col-0) and an A. thaliana mutant (vtc1) deficient in ascorbate. Spectrophotometrical quantification has shown that this mutant has a higher content of glutathione during plant development compared with Col-0 [Pavet V, Olmos E, Kiddle G, Mowla S, Kumar S, Antoniw J, et al. Ascorbic acid deficiency activates cell death and disease resistance responses in Arabidopsis. Plant Physiology 2005;139:1291-03]. We have observed, using immunolabelling techniques, that mitochondria showed the highest density of glutathione labelling in both Col-0 and vtc1 plants during all developmental stages and that the lowest density occurred in the chloroplasts, for both lines. However, the distribution of glutathione in the different sub-cellular compartments indicates that the chloroplasts contain about 62-75% of the total cellular glutathione and that the mitochondria represent the second greatest pool, with about 15-25% of the total cellular glutathione. It has been observed previously that the vtc1 mutant exhibits an induction of cell death and disease resistance in the face of pathogen attack. The differing distributions and concentrations of glutathione in the mitochondria of wild-type A. thaliana and the vtc1 mutant is discussed.