Despite the studies performed in the last 2 decades on oesophageal or gastrointestinal function and sleep parameters, we continue to have limited knowledge of how sleep interferes with gastrointestinal physiology. In general, pHmetry is used to monitor circadian gastro-oesophageal reflux activity, and 24-h analysis evaluates upright and supine position. The reflux activity recorded during upright periods is generally referred to as awake refluxes, while supine refluxes are considered nocturnal and related to sleep. From a clinical point of view, nocturnal heartburn is evaluated as a main sign of nighttime reflux, and the prevalence of such symptoms has been reported around 74% among patients suffering from chronic heartburn. Recent studies have shown the importance of nighttime gastro-oesophageal reflux in the development of oesophagitis and other extraoesophageal complications, and adenocarcinoma of the oesophagus. In a national population-based telephone interview survey of 1000 adults conducted in USA, 13% of the respondents reported experiencing heartburn only during nighttime, 20% reported heartburn during daytime only, while 65% of respondents experienced heartburn both day and night. Another important issue is the role of nighttime reflux events in the pathohgenesis of respiratory and aerodigestive tract diseases, such as pharyngitis, sinusitis, laryngitis, chronic bronchitis, and asthma, among patients with gastro-oesophageal reflux diseases (GORD). Supraoesophageal complications have not been systematically studied but great relevance has been given to the oesophageal clearance of nighttime reflux. Indeed, while upright refluxes (experienced during waking) tend to be short and to resolve quickly, supine refluxes (experienced during sleep) tend to be longer and to resolve more slowly. In addition the noxious effect of acid content on the tracheobronchial tree has been recently studied to evaluate upper oesophageal sphincter function during sleep. Indeed, this research shows that the pressure of this sphincter appears related to different phases of sleep, although it overall decreases during sleep. A relevant aspect is the negative influence of nighttime refluxes on sleep and, consequently, on most personal, occupational and social activities the following day. The socioeconomic consequence of these disturbances could be significant, which underlines the need for correct therapeutic strategies to deal with chronic nocturnal heartburn. This summary underlines some viewpoints regarding the studies made on GOR during sleep. However some questions do emerge from these studies. The aspects mentioned above mainly refer to a symptomatic nocturnal reflux; so the question that remain are: Which is the meaning of instrumentally recorded gastro-oesophageal refluxes alone? Are there differences between the refluxes recorded in the supine position during sleep or during awake periods? Can the discrimination between refluxes during wake and asleep states help the clinician better define the management of GORD? A study authored by Dickman et al. in this issue of Neurogastroenterology and Motility suggests that the principal characteristics of acid refluxes events in supine-awake periods resemble more closely those Address for correspondence Prof. Rosario Cuomo M.D. Gastroenterological Unit, Department of Clinical and Experimental Medicine, University of Naples ‘‘Federico II, Via Sergio Pansini 5, 80131 Naples, Italy. Tel. and fax: +39 0817463892; e-mail: rcuomo@unina.it Received: 5 July 2007 Accepted for publication: 10 July 2007 Neurogastroenterol Motil (2007) 19, 701–703 doi: 10.1111/j.1365-2982.2007.00993.x