We thank Drs Su and Chou for their interest in our recent article in CHEST (July 2010),1 and submit our response to the comments made. We would like to clarify that although our study did demonstrate a rise in markers of coagulation and serum IL-6 in response to hypoxic challenge, such an association does not necessarily imply a causal relationship. We accept that the origin for the rise in serum IL-6 in response to hypoxia is not clear and, moreover, may not necessarily reflect a rise in IL-6 at the tissue level. We agree with the authors that respiratory muscles may be a possible source for increased IL-6 release as a consequence of hypoxia stimulating ventilation. Indeed, our department has demonstrated a rise in serum IL-6 in response to exercise in patients with cystic fibrosis.2 However, given the modest rise in respiratory rate in the patients undergoing hypoxic challenge, it would seem unlikely that the increased load on respiratory muscles could solely account for the rise in serum IL-6. A number of other studies have similarly demonstrated a rise in serum IL-6 and other inflammatory markers in response to hypoxia,3,4 although the exact mechanism for this association is yet to be elucidated.