Glutathione (GSH) conjugates of 4-hydroxy-trans-2,3-nonenal (HNE) are the final products of lipid peroxidation. In the present study, the role of multidrug resistance-associated protein 2 (MRP2) in biliary excretion of GSH conjugates of HNE (HNE-SG) was studied in vitro by using Madin-Darby canine kidney II (MDCK II) cells expressing human MRP2 and in vivo using a mutant rat strain whose MRP2 expression is defective (Eisai-hyperbilirubinemic rats [EHBR]). A high-performance liquid chromatography method was developed to assay HNE-SG conjugates. Four diastereomeric HNE-SG conjugates could be separated with this method. Three of four HNE-SG conjugates were detectable after incubation of the cell monolayers with HNE. Expression of human MRP2 resulted in a 10-fold increase in HNE-SG conjugates excretion across the apical membrane of MDCK II cells. The four HNE-SG conjugates appeared swiftly in bile from Sprague Dawley rats after intravenous administration of HNE, whereas no detectable HNE-SG conjugates were observed in the bile of EHBR. These results demonstrate the role of MRP2 in the biliary excretion of HNE-SG conjugates.