Hyperkalemia is potentially lethal, and possibly more so in patients with end-stage renal disease, because of underlying cardiovascular disease. The aim of this study was to determine the effect of chewing tobacco on serum potassium levels in an adult maintenance hemodialysis patient. The patient was asked to discontinue the use of chewing tobacco for 3 weeks. Serum potassium levels were drawn during this time period and compared with values before tobacco discontinuation. The potassium content of the tobacco was measured at 570 mg/oz. Serum potassium values decreased after elimination of the chewing tobacco and there were no hospitalizations for hyperkalemia compared with the four hospitalizations for hyperkalemia that occurred over a 6-month period before discontinuation. Chewing tobacco contains a significant amount of potassium. In this first report of the effect of chewing tobacco use on serum potassium levels in a patient with end-stage renal disease, improved potassium levels occurred once the tobacco was eliminated. The use of chewing tobacco should be used in a screen of unexplained hyperkalemia.