Water transport is an important consideration in the optimization of polymer electrolyte fuel cell (PEFC) performance, affecting both internal resistance and cathode polarization losses. Novel experiments are described using neutron radiography to measure water gradient profiles within Nafion(R) in an operating PEFC. Preliminary neutron intensity gradients show qualitative agreement with the expected response of membrane water content to changes in feed gas humidification and fuel cell current. Previous experimental measurements of similar water gradients have generally relied on "integral" measurements such as ac impedance spectroscopy which cannot probe details of the gradient within the membrane. This is one of the first "differential" measurements of water gradients within Nafion.