The air sac functional anatomy of sulphur-crested cockatoos (Cacatua galerita) during isoflurane anesthesia was studied by evaluation of respiratory casts of sulphur-crested cockatoos, blood gas analysis, and air sac gas analyses. The air sac anatomy of the sulphur-crested cockatoo was different from that described previously in nonpsittacine bird species, with more extensive cranial and caudal thoracic air sacs and smaller abdominal air sacs. Blood gas analysis results indicated arterial and venous hyperoxia as a result of using 100% O₂ as the anesthetic carrier gas, the significance of which in birds is currently unclear. Cranial and caudal thoracic air sac oxygen and carbon dioxide partial pressures (Po₂ and Pco₂, respectively) were similar to those previously described in birds ventilated with 100% O₂. Clavicular air sac Po₂ and Pco₂ were significantly lower than the cranial thoracic air sac, indicating significantly less ventilation of the clavicular air sac than of either the cranial or caudal air sacs.