Novel proton-conducting polyurethanes based on poly(tetramethylene glycol), with the protons being incorporated in the flexible soft segments, were prepared and their structure-property relationships were investigated. The structure: and the morphology were studied by means of differential scanning calorimetry (DSC), and wide- and small-angle X-ray scattering (WAXS and SAXS). Molecular mobility and proton conductivity were measured by means of broadband dielectric relaxation spectroscopy (DRS, 10(-2)-10(9) Hz) and of thermally stimulated depolarisation currents techniques (TSDC, 77-300 K). Dc conductivity values, sigma (dc), determined from ac conductivity and from complex impedance plots, are of the order of 10(-5) S/m at 50 degreesC, and decrease with increasing hard segment content of the polyurethanes. Their temperature dependence is described by Vogel-Tammann-Fulcher-Hesse (VTFH), suggesting that the conductivity mechanism is governed by the motion of the polymeric chains.