Sodium polystyrene sulfonate (SPS), an ion-exchange resin designed to bind potassium in the colon, was approved in 1958 as a treatment for hyperkalemia by the US Food and Drug Administration, 4 years before drug manufacturers were required to prove the effectiveness and safety of their drugs. In September 2009, citing reports of colonic necrosis, the Food and Drug Administration issued a warning advising against concomitant administration of sorbitol, an osmotic cathartic used to prevent SPS-induced fecal impaction and to speed delivery of resin to the colon, with the powdered resin; however, a premixed suspension of SPS in sorbitol, the only preparation stocked by many hospital pharmacies, is prescribed routinely for treatment of hyperkalemia. We can find no convincing evidence that SPS increases fecal potassium losses in experimental animals or humans and no evidence that adding sorbitol to the resin increases its effectiveness as a treatment for hyperkalemia. There is growing concern, however, that suspensions of SPS in sorbitol can be harmful. It would be wise to exhaust other alternatives for managing hyperkalemia before turning to these largely unproven and potentially harmful therapies.