The electrosynthesis of polyalkylenedioxythiophenes is described, starting with the anodic oxidation of 3,4-ethylenedioxythiophene (1) or 3,4-trimethylenedioxythiophene (2). The resulting polymers are extraordinarily stable during charging and discharging. Owing to a narrow band gap, the first long-wavelength absorption in the doped state appears above 900 nm.