Many avian species exhibit an extraordinary ability to exercise under hypoxic condition compared with mammals, and more efficient pulmonary O₂ transport has been hypothesized to contribute to this avian advantage. We studied six emus (Dromaius novaehollandaie, 4-6 mo old, 25-40 kg) at rest and during treadmill exercise in normoxia and hypoxia (inspired O₂ fraction  0.13). The multiple inert gas elimination technique was used to measure ventilation-perfusion (/) distribution of the lung and calculate cardiac output and parabronchial ventilation. In both normoxia and hypoxia, exercise increased arterial PO₂ and decreased arterial PCO₂, reflecting hyperventilation, whereas pH remained unchanged. The / distribution was unimodal, with a log standard deviation of perfusion distribution = 0.60 ± 0.06 at rest; this did not change significantly with either exercise or hypoxia. Intrapulmonary shunt was <1% of the cardiac output in all conditions. CO₂ elimination was enhanced by hypoxia and exercise, but O₂ exchange was not affected by exercise in normoxia or hypoxia. The stability of / matching under conditions of hypoxia and exercise may be advantageous for birds flying at altitude.