A multi-instrumented single polymer exchange membrane fuel cell is tested. it allows measuring local current densities and the temperature field along the gas channels. It is built from transparent PMMA so that an additional observable is the location where liquid water appears in the channels. Some local and transient observations are presented. A result is that the temperature field is strongly correlated with the current density distribution and it is confirmed that both depend strongly on water management. Some local aging effects and the observation of internal currents in open circuit conditions are reported. (C) 2008 Elsevier B.V. All rights reserved.