*Division of Molecular Biology,

The human multidrug resistance–associated protein MRP confers resistance to various cytotoxic drugs by lowering the intracellular drug concentration. Recent evidence indicates that MRP can also transport glutathione S– conjugates across membranes. To study the transport properties of MRP in intact cells, we have expressed human MRP cDNA in the polarized pig kidney epithelial cell line LLC-PK1. MRP mainly localized to the basolateral plasma membrane of these cells, and not to the apical membrane, as deter-mined by immunocytochemistry using confocal laser scan-ning and electron microscopy. In accordance with this local-ization, MRP caused increased transport of the glutathione