A two-cell theory is developed to measure proton exchange membrane (PEM) resistance to proton flow during conduction through a PEM fuel cell. The theoretical framework developed herein is based upon fundamental thermodynamic principles and engineering laws. We made appropriate corrections to develop the theoretical model previously proposed by Babu and Nair (B.V. Babu, N. Nair, J. Energy Edu. Sci. Technol. 13 (2004) 13-20) for measuring membrane resistance to the flow of protons, which is the only ion that travels from one electrode to the other through the membrane. A simple experimental set-up and procedure are also developed to validate the theoretical model predictions. A widely used commercial membrane (Nafion (R)) and several in-house membranes are examined to compare relative resistance among membranes. According to the theory, resistance of the proton exchange membrane is directly proportional to the time taken for a specific amount of protons to pass through the membrane. A second order differential equation describes the entire process. The results show that theoretical predictions are in excellent agreement with experimental observations. It is our speculation that the investigation results will open up a route to develop a simple device to measure resistance during membrane manufacturing since electrolyte resistance is one of the key performance drivers for the advancement of fuel cell technology. (C) 2007 Elsevier B.V. All rights reserved.