The glutathione reductase (GR; EC 1.6.4.2) isozyme present in peroxisomes has been purified for the first time, and its unequivocal localization in these organelles, by immunogold electron microscopy, is reported. The enzyme was purified c. 21-fold with a specific activity of 9523 units mg(-1) protein, and a yield of 44 microg protein kg(-1) leaves was obtained. The subunit size of the peroxisomal GR was 56 kDa and the isoelectric point was 5.4. The enzyme was recognized by a polyclonal antibody raised against total GR from pea (Pisum sativum) leaves. The localization of GR in peroxisomes adds to chloroplasts and mitochondria where GR isozymes are also present, and suggests a multiple targeting of this enzyme to distinct cell compartments depending on the metabolism of each organelle under the plant growth conditions. The expression level of GR in several organs of pea plants and under different stress conditions was investigated. The possible role of peroxisomal GR under abiotic stress conditions, such as cadmium toxicity, high light, darkness, high temperature, wounding and low temperature, is discussed.