We present Viking observations of energetic electrons and ions which move upward along the magnetic field lines with energies of the same order of magnitude. The field-aligned particles are associated with a strong broadband low-frequency turbulence in the electric field and with downward Birkeland currents. We suggest that both ions and electrons are accelerated by a time-varying field-aligned electric field component. The downward field component accelerating the electrons upward is experienced as quasi-static by the electrons while they remain in the height-limited acceleration region. For the ions the fluctuating field is a wave field which has only a small translational effect on them. ¿ American Geophysical Union 1988