['Multidrug resistance (MDR) has a potentially serious influence on cancer treatment and should be taken into consideration in the design and application of therapeutic regimens. It is mediated through the activity of cellular pumps.', 'To investigate whether furosemide, itself a pump-blocker, reverses MDR in an in vitro model.', 'An MDR bladder cancer cell line (MGH-u 1R) and its parental (drug sensitive) clone were exposed to epirubicin and furosemide, with the concentration of one drug fixed and that of the other serially diluted in a 96-well plate format. Both drugs formed the variable component in separate experiments. After a 1-h exposure, the cells were washed and replenished with fresh medium. To examine the toxicity of epirubicin and furosemide separately and in combination, monotetrazolium-based assays were carried out. Intracellular epirubicin distribution was assessed by confocal microscopy as a second index of resistance status after in vitro exposure.', 'MGH-u 1R cells incubated with furosemide showed distribution of drug similar to that in the parental cells (MGH-u 1 sensitive). Controls (without furosemide) continued to show a resistant pattern of fluorescence. In cytotoxicity assays furosemide appeared substantially non-toxic. Resistant cells in the toxicity titration experiments showed increased resistance to levels of furosemide over 500 mug/ml. Parental cells were made only marginally more sensitive against increased background toxicity.'] Does furosemide reverse multidrug resistance status in bladder cancer cells in vitro?