Simultaneous measurements of magnetic fields and soft particle distributions in the topside auroral ionosphere reveal the relationships between field-aligned currents and primary and secondary auroral particles. In the evening MLT sector the region 2 field-aligned currents, which are directed into the ionosphere, are found to extend on the average 2.4¿ of invariant latitude equatorward of the low-latitude boundary of 1-keV electron recipitation from the magnetospheric plasma sheet. This current system is found to lie within the mid-latitude total ion trough, as defined by its topside density depletion. This is a region predominantly void of particles between 5 eV and 15 keV. The current carriers are inferred to be upward flowing cold ionospheric electrons. At higher latitudes in the premidnight sector the region I field-aligned current system lies within the region of particle precipitation and terminates at its high-latitude boundary coincidently with the termination of energized precipitating particle fluxes. The primary reversal from downward to upward flowing field-aligned currents may be quite sharp or may occur over several degrees of latitude. The current reversal is not necessarily associated with any particular particle precipitation structure.