This invention is concerned with human organic anion transporter ("hOAT"). Isolated nucleic acid encoding hOAT is provided, along with isolated hOAT polypeptide. hOAT nucleic acid and/or hOAT polypeptide are employed in transgenic animals, recombinant cells, replicable vectors and analytical procedures for identifying hOAT agonists or antagonists, assays for identifying hOAT alleles and/or isotypes, screening tests for nephrotoxic or neurologically active compounds, and determination of drug-drug interactions within the kidney or brain.