Multidrug resistance (MDR) is a cause of treatment failure in many cancer patients. MDR refers to a phenotype whereby a tumor is resistant to a large number of natural chemotherapeutic drugs. Having prior knowledge of the presence of such resistance would decrease morbidity from unsuccessful therapy and allow for the selection of individuals who may benefit from co-administration of MDR inhibiting drugs. The Tc-99m labeled single photon emitting radiotracers sestamibi and tetrofosmin have shown some predictive value. However, positron-emitting (PET) radiotracers, which allow for dynamic, quantitative imaging, hold the promise of more accurate and specific identification of MDR tumors.