Early-stage sarcoidosis usually does not produce abnormalities, such as hypoxemia or hypercapnia, on arterial blood gas. Sarcoidosis-associated PH and severe fibrocystic disease may cause significant hypoxemia.31 However, hypercapnia is rarely observed in end-stage fibrocystic sarcoidosis. There is actually a paucity of information concerning resting arterial Pco2 in sarcoidosis, and most of the information is decades old. Resting hypercapnia was not found to be present in a group of 63 patients with pulmonary sarcoidosis, including some with advanced pulmonary sarcoidosis.32 In addition, at least in radiographic stage 1 through stage 3 sarcoidosis, the dead space-tidal volume ratio appears to remain normal.33 We suspect that the rare presence of hypercapnia except in the most severe pulmonary sarcoidosis probably mirrors the situation in other interstitial lung diseases, in which the hypoxic drive is usually maintained and the ventilatory drive may be augmented by decreased lung compliance. In patients who suffer from advanced respiratory failure, the presence of hypercapnia rarely presents a diagnostic challenge. If hypercapnia is found in a patient with sarcoidosis without severe pulmonary dysfunction, then alternative causes of hypercapnia, such as hypothyroidism, the use of medications that blunt respiratory drive, and SDB, should be investigated.