Performances of a H2/O2 polymeric electrolyte fuel cell running at 80°C under 3 bars of gas pressure and using a new filled thermostable ionomeric membrane [sulfonated polysulfone (SPS) filled with phosphatoantimonic acid particles] are analysed with a recent experimental method established for impedance measurements of electrochemical batteries during discharge. A classical impedance-measurement set controls under sinusoidal current perturbation a PEMFC connected in parallel to the load into which it discharges. The impedance diagrams present at high frequencies an inductive behaviour analogous to that observed for batteries, one or two capacitive arcs. The internal resistance of the PEMFC can be estimated. The results demonstrate the possibility to study with classical equipment the impedance of high-capacity and low-impedance FC during their discharge through a constant load.