Poly(p-phenylene) is a conjugated polymer that becomes conductive after doping. It has been demonstrated that the amorphous polymer lightly doped with iron(III) chloride exhibits both electronic and ionic conductivity in the range 10(-8-)10(-5) S/cm. Annealing the pristine amorphous polymer and doping it to the same level leads to a partially crystalline material, the exclusively electronic conductivity of which is one order of magnitude higher. The relative dielectric constant, however, seems to be unaffected by the polymer structure. The temperature dependencies of both components of the conductivity were measured giving similar values of activation energies within the range 0.29-0.36 eV. (C) 2000 Elsevier Science B.V. All rights reserved.