SUMMARYMethaemoglobinaemia is rare but should be considered in cases of cyanosis unresponsive to oxygen therapy. An example of this is given involving the accidental ingestion of Amyl Nitrite. CASE REPORTA 20-year-old girl attended the accident and emergency department following a collapse. She was alert and orientated, but complained of headache. Her blood pressure was 80/40 mmHg. Her most striking feature was a blue-grey discolouration of her skin. Oxygen therapy made no difference to her appearance, although blood gas analysis revealed a Pao2 of 46 kPa.She had been attending a Halloween party, but was not wearing make-up, and admitted taking 'Poppers' (Amyl Nitrite). Instead of inhaling the vapour, she had swallowed the liquid. Amyl Nitrite may produce methaemoglobinaemia, and this was confirmed by analysis of her blood which revealed a value of 30% methaemoglobin. When dropped on to a white sheet, a sample of her blood produced the characteristic chocolate colouration, which is a qualitative test for methaemoglobin. Gastric lavage was performed and she was resuscitated with intravenous colloid and intravenous Methylene Blue. No further complications followed and she was discharged the following day. DISCUSSIONMethaemoglobinaemia is characterized by increased amounts of haemoglobin where