Multidrug resistance proteins (Mrps) are ATP-driven export pumps that mediate the export of organic anions from cells. So far only little information is available on expression and physiological functions of Mrps in brain. The expression of mRNAs of six Mrp paralogs in rat brain, as well as in rat cultures enriched for neurones, astrocytes, oligodendrocytes and microglial cells, was studied by qualitative and semiquantitative RT-PCR analysis. In adult rat brain as well as in neural cell cultures the mRNAs coding for Mrp1, Mrp3, Mrp4 and Mrp5 were detected. Semiquantitative analysis revealed that the mRNAs coding for Mrp1 and Mrp5 were more abundant in the four cell culture types than mRNAs of the other Mrps. mRNAs coding for Mrp3 and Mrp4 were found at significant levels in cultured astrocytes and microglial cells, whereas cultures of neurones and oligodendrocytes contained only marginal quantities of these mRNAs. Putative physiological functions of Mrps in brain cells are discussed.