Saltpeter ingestion. A 37-year-old man presented to the emergency department after an attempt to self-treat his priapism with saltpeter (K+NO3). Initially he had a potassium of 7.6 with electrocardiographic changes and a markedly elevated CO2. The potassium and carbon dioxide normalized in less than 24 hours with standard treatment for hyperkalemia. Hyperkalemia is expected with large oral potassium ingestion; and the elevated CO2 was spurious, caused by the misreading of serum nitrates by the Ektachrom 700 system. Ingestion of K+NO3 should be added to the differential of hyperkalemia with a markedly elevated CO2. 