In two cases with drug-related hyperkalemia, potassium homeostasis, causes, symptoms and therapy are discussed. Iatrogenic and therefore avoidable hyperkalemia occurs most often when potassium, ACE-inhibitors, nonsteroidal antiinflammatory drugs or potassium-sparing diuretics are administered in patients with impaired renal function or diabetes mellitus. The emergency treatment in patients with severe hyperkalemia consists of intravenous calcium injections, infusion of glucose with insulin and, more recently, salbutamol. With acidotic patients administration of sodium-bicarbonate can be tried. Ion-exchange drugs and furosemide have a more delayed effect. With oliguria and anuria hemodialysis is often necessary.