Finding of low oxygen saturations is common in the emergency department and usually managed with oxygen therapy. However, persistently low oxygenation despite oxygen therapy can present as a diagnostic and management challenge. We present the case of a 4-year-old boy who presented with low oxygen saturations and signs of intravascular haemolysis. After extensive investigation, the cause was concluded to be methaemoglobinemia with glucose-6-phosphate dehydrogenase deficiency-induced haemolysis. We conclude that the diagnosis of methaemoglobinemia should be considered in a patient who presents with the triad of low oxygenation without respiratory distress and clear lung fields on auscultation and chest x-ray.