Rubidium-86 is commonly used as a tracer of potassium and can be used for rubidium uptake assays. Rb-86 is one of the highest energy (beta or gamma emitting) radionuclides encountered in UM research laboratories, although not routinely, and requires special care. Rubidium Rb-86 was used to measure of the endocardial distribution of left ventricular coronary blood. Besides, this agent was studied in Duchenne muscular dystrophy in the detection of carriers of the gene. In addition, Rb-86 participated in a clinical trial in patients with benign breast lesions, and stage I/II, stage III/IV untreated breast cancers to study its uptake by the red blood cell (RBC). It was found that the RBC potassium content was slightly increased in the cancer patients and was suggested that the decreased uptake is a cancer-related phenomenon.