The diagnosis of gastroesophageal reflux is sometimes challenging, especially when symptoms are unresponsive to high-dose acid suppression. With the advent of new technology it is possible to detect and quantify nonacid or weakly acidic reflux. Multichannel intraluminal impedance (MII), introduced over 10 years ago, is gaining popularity as a reflux detection tool. The ability to detect nonacid or weakly acidic reflux events, aerophagia, and to discern true reflux events from swallows could make it more a powerful tool than pH detection alone. This is a review of the role of MII as it pertains to the diagnosis of GERD and related disorders. Studies done on normal subjects and in GERD reveal that nonacid or weakly acidic reflux occurs frequently. Several studies have been published that document types and frequency or reflux episodes comparing pH to MII. pH electrodes fail to detect the majority of nonacid or weakly acidic reflux events. MII has revealed nonacid reflux to be less common in untreated GERD subjects than in normal subjects. GERD subjects have greater degrees of liquid-type reflux events compared to normal subjects who have more gas-type reflux events. In treated GERD subjects and normal subjects, proton pump inhibitors do not seem to decrease the amount of reflux but render the reflux nonacid or weakly acidic in nature. Recently work evaluating atypical symptoms of GERD with MII has been published.