The stability of electrostatic waves with frequencies near the hydrogen cyclotron frequency is investigated for an auroral plasma containing an ion beam. The energetic portion of the model distribution function is based on measurements made by Aerospace ion and electron detectors on the S3-3 satellite at an altitude of 1 RE. Parameters describing unmeasured cold background species are varied, and the resulting wave growth rates are compared with measurements from the Berkeley AC electric field experiment. The events studied in this report involve waves that peak just above the hydrogen cyclotron frequency. These waves are seen only when an upgoing ion beam is present. We conclude that of the wave modes investigated, only electrostatic hydrogen ion cyclotron waves can be driven by the existing plasma. The waves can be produced either by drifting electrons or by the ion beam. Although we cannot exclude the possibility that electrons are drifting and contributing to wave growth, we find that many features of the measurements are a natural consequence of instabilities generated by ion beams. In this model, ion beams are seen with their observed temperatures because they have evolved to a weakly unstable configuration in which the wave growth length is comparable to the width of the beam region. Waves are well confined to the beams because they are damped rapidly in the adjacent plasma. The mirror effect can maintain a weak instability over a considerable altitude range. The above explanation is consistent only if we make two assumptions concerning unmeasured particles. First, hydrogen ions that are too cold to be measured by the S3-3 detectors must be present to sustain the hydrogen cyclotron waves and to produce a second peak in the ion distribution function. In addition, we require that almost no cold Maxwellian electrons are present because they would Landau damp the waves more rapidly than the ion beam can drive them. The measurements provide some indication that electrons have been heated to just above the temperature at which they no longer damp the waves. The above assumptions appear to be reasonable if the satellite is passing above a region containing parallel electric fields. The electric field accelerates beam ions up. Cold ionospheric electrons are reflected down so they cannot reach the satellite. In this environment, wave growth is balanced between a resonance in the parallel ion beam velocity where ∂f/∂v>0 and ion cyclotron damping, which is also generated by the ion beam. That is, the apparent effect of the EHC (electrostatic hydrogen ion cyclotron) waves is to convert parallel ion beam energy to perpendicular ion beam energy. If this effect proves to be generally true, a source for strong pitch angle scattering has been found, and the nonexistence of downgoing ion beams has been explained.