The potassium level of patients using diuretics, particularly the elderly, should be monitored (to detect either hypo- or hyperkalaemia). Diuretic-induced hypokalaemia is rather rare because diuretics are often combined with an ACE inhibitor or an ATR blocker. Identify and correct hypokalaemia in patients with diarrhoea and vomiting. If the patient has unexplained hypokalaemia remember renal diseases, subtle vomiting and bulimia as well as primary aldosteronism, i.e. Conn's syndrome. Consider magnesium deficiency as a cause of therapy-resistant hypokalaemia .