Incorporation of a ligand into polyvinylchloride allows the production of ion selective electrodes that are soft-bodied and disposable. With features make them especially suitable for clinical, particularly gastroenterological, investigations. We report here on the construction of a combined reference and pH electrode suitable for use at jejunal biopsy. With this type of pH electrode, the pH of the mucosal surface of the jejunum in UK and in Indian subjects, without evidence of upper gastrointestinal disease, was about pH 6.0. This was almost identical to previous values measured using a separate reference electrode. Both the polymer electrode and a suitable data logger can be conveniently produced in the laboratory and compare favourably with commercially available systems, provided the range of pH likely to be encountered is within the operating range of the incorporated ligand.