Multidrug resistance-associated protein (MRP) actively transports a broad range of anionic compounds out of the cell. To date, six different homologues of MRP (i.e. MRP1–MRP6) have been identified. The current study examines the expression of the various MRP homologues in both primary cultured bovine brain microvessel endothelial cells (BBMEC) and the capillary-enriched fraction from bovine brain homogenates. RT–PCR analysis demonstrated the presence of MRP1, MRP4, MRP5 and MRP6 in both BBMEC and the capillary-enriched fractions of brain homogenates. While low levels of MRP3 were detected in the BBMEC, it was not observed in the capillary-enriched fraction. In addition, RT–PCR and Western blot studies indicated an absence of MRP2 expression in both blood–brain barrier preparations. The presence of several different MRP homologues in the brain microvessel endothelial cells may be important in controlling the permeability of the blood–brain barrier to organic anions.