The Dubin-Johnson syndrome is characterized by an patocytes into the bile. 3,4 This defect results in predomiinherited defect in the secretion of amphiphilic anionic nantly conjugated hyperbilirubinemia and a characterconjugates from hepatocytes into the bile. We have re-istic secondary rise of intravenously administered cently identified the membrane protein mediating the sulfobromophthalein in blood plasma following its conadenosine triphosphate (ATP)-dependent transport of jugation with glutathione in hepatocytes and transport glutathione and glucuronate conjugates as a multidrug-of the conjugate from hepatocytes to the blood. 3-9 Macresistance protein (MRP) and localized it to the canalicu-roscopic examination of the liver from patients with lar as well as to the lateral hepatocyte plasma memDubin-Johnson syndrome shows it to be intensely pigbrane. In the present study we show the selective mented with an appearance described as grossly black 2 absence of the canalicular isoform of MRP (cMRP) from the hepatocytes in a patient with Dubin-Johnson syn-or dark blue. 10 Several most useful animal models of drome by double-label immunofluorescence and confo-this defect in human hepatobiliary transport have been cal laser scanning microscopy using antibodies di-described and extensively studied. 3,[11][12][13][14][15][16] In the transrected against MRP and dipeptidyl-peptidase IV port-deficient GY/TR 0 mutant Wistar rat 11 a selective (DPPIV). Another isoform of MRP was detected, how-canalicular defect in the ATP-dependent transport of ever, in the lateral hepatocyte membrane of the pa-glutathione S-conjugates and other nonbile salt organic