The high-altitude plasma instrument on board the DE 1 satellite was operating during several near crossings of the auroral kilometric radiation (AKR) source in the nightside auroral region. Observations of electron distributions indicate a region of perpendicular heating (T⊥/T∥>10) adjacent to and within the source region. Loss cones, trapped particles, beams, and electron conical distributions are also observed near and within the source region, which extends perpendicular to the magnetic field line for at least 20 km. Near the AKR source region wave-particle interactions appear to have modified the observed electron distributions. We compare the observations to those predicted by recently published numerical simulations. ¿ American Geophysical Union 1993