Novel composite electrode structures have been fabricated by single-step electropolymerization of polypyrrole onto a porous graphite fiber matrix. The graphite substrate provides a lightweight structure with high surface area. The available charge capacity of the composite electrodes was proportional to the electropolymerization merization time and the mass of electroactive polymer with reversible charge capacities in excess of 4.0 C cm(-2) and aspecific capacity of 90 mAh g(-1), independent of polymer mass. The rate of charge extraction was dependent on the polymer mass and the morphology of the polymer electrode. In test cells using a polypyrrole/graphite fiber anode and a polypyrrole-polystyrene sulfonate/graphite fiber cathode, we have demonstrated a capacity of more than 40 mAh g(-1) based on the active mass of the undoped polymer on discharging the cell to 0.1 V over a 10 k Omega load. More than 70% of the available charge was extracted from the cell over 50 cycles with no degradation of cell performance.