Probenecid is used as a uricosuric agent in the treatment of chronic gout and as an adjunct to enhance antibiotic levels in the blood. For research purposes, it is used as a prototypic inhibitor of organic anion transporters and MRPs, including MPR2. The purpose of this research is to study the interaction of probenecid with two other important transporters of the ATP-binding cassette family, Breast Cancer Resistance Protein (BCRP) and P-glycoprotein. These drug efflux transporters are present in the intestine, liver and other organs, and they affect the bioavailability of many compounds. Using the polarized canine kidney cell line MDCK-II and its human MDR1-, BCRP- and murine Bcrp1-transduced subclones, we found that probenecid is transported by mouse Bcrp1 and human BCRP, but not by P-glycoprotein. In addition, flow cytometry experiments showed that probenecid did not affect the accumulation of mitoxantrone in Bcrp1- and BCRPtransduced cells, indicating that this compound was not an effective BCRP/Bcrp1 inhibitor at the concentrations used. We conclude that probenecid is a good substrate of BCRP/Bcrp1, suggesting potential interaction with BCRP/Bcrp1 inhibitors.