An older patient who was being treated with ramipril, chlorpromazine and aspirin presented with hypotension and serum sodium of 119 mmol/litre. The patient was treated with intravenous saline and all drug therapy was stopped. Serum sodium rose following fluid therapy. Ramipril was restarted as the patient's blood pressure increased. Serum sodium dropped to 112 mmol/litre. The patient's thyroid and adrenal functions were within normal limits, as were liver function tests and C-reactive protein. The hyponatraemia corrected when the patient was placed on fluid restriction and treatment with ramipril stopped.