Prone positioning of patients with acute respiratory failure was first suggested over 30 years ago. In the present issue of Clinical Science, Reutershan and co-workers have studied the changes in end-expiratory lung volume in 12 patients with ARDS (acute respiratory distress syndrome) over an 8 h period following manual turning from the supine to prone position. From the data presented, the authors suggest that baseline end-expiratory lung volume could be used to identify responders, and serial measurements would permit appropriate 'dosing' of the therapy. Although this is an interesting study that provides data that have rarely been collected when assessing the response to prone positioning, there are a number of limitations that need to be considered. However, despite the limitations, the study does stimulate a number of important questions related not only to the use of the prone position, but also to the management of patients with ARDS in general.