Nutritional support in the critically ill is commonly delivered via a nasogastric tube. Correct positioning in the stomach must first be confirmed as inadvertent feeding into the lungs carries a high risk of mortality. The National Patient Safety Agency (2005) recommends the method of pH testing nasogastric tube aspirates to verify tube position. This article critically analyses the research supporting this method, and questions its reliability in critically ill patients whose gastric pH may well be altered due to prophylactic stress ulcer medications and continuous feeding regimens. There is a lack of quality research testing this method in the critically ill population. The theory-practice gap is addressed, and preliminary research behind use of techniques such as capnography and capnometry is also examined.