S3-3 satellite observations of low altitude electrostatic shocks on auroral zone field lines indicate the presence of parallel electric fields below an altitude of 2000 km and probably below 1100 km. These conclusions result from the direct observation of parallel fields, from inference based on the V-shaped equipotential contours associated with some shocks, and from the fact that perpenducular fields with magnitudes as large as those observed in shocks are not seen in the ionosphere.