Gastric potential difference (GPD) is used increasingly as an index of mucosal integrity. The technique for GPD measurement currently employed is however laborious due to the preparation and check of KCl-agarose bridges prior to each experiment. In addition, calculations - usually handmade - are time-consuming and inaccurate. Therefore, a new apparatus allowing continuous recording of basal and drug-induced changes in GPD values was developed. A commercially available 24-hour pH monitor (Proxima Light, Synectics Medical) was modified in order to allow GPD measurement and recording with subsequent elaboration of data. Furthermore, simultaneous measurement of GPD and intragastric pH through the use of a single stomach probe was made possible. The new method was checked towards the classical PD measuring system employing KCl-agarose bridges. The readings obtained with both systems, either in basal conditions or after aspirin, correlated in a highly significant way. Readings proved to be quite stable with a variation, for 150 consecutive values, of less than 2 mV. With this system the effect of pH modifications, obtained through H2 receptor stimulation and inhibition, on the behaviour of GPD values was investigated in healthy volunteers. Analysis of paired data obtained from these experiments showed an inverse relationship between these two parameters. This suggests that GPD and pH should be measured together, especially during experiments aiming to study drug effects on gastric mucosa. Although the apparatus described was developed for PD measurement and recording in the stomach, it can be used easily for PD measurement across the mucosa of the entire digestive tract, for example in the esophagus, colon or rectum.