Rhodamine 123 is efficiently effluxed in mBMDC/67NR-Hyg clones. Rhodamine 123 efflux was assayed to prove whether Abcb1a/Abcb1b up-regulation in mBMDC/67NR-Hyg clones was functional. Cells were loaded with Rhodamine 123 and analyzed for the remaining cellular Rhodamine 123 content after 40 minutes by flow cytometry. The side-population (SP) population, representing cells, which have effectively effluxed Rhodamine 123, are marked by an arrow. Verapamil was used to specifically block Abcb1a/Abcb1b multidrug transporters. Flow cytometry data revealed that Rhodamine 123 is efficiently effluxed in mBMDC/67NR-Hyg clones; an effect, which was completely blocked by verapamil.