Electromagnetic ion cyclotron waves generated by 10--50 keV protons in the Earth's equatorial magnetosphere will interact with the ambient low-energy ions also found in this region. We examine H+ and He+ distribution functions from ≈1 to 160 eV using the Hot Plasma Composition Experiment instrument on AMPTE/CCE to investigate the thermal ion response to the waves. A total of 48 intervals were chosen on the basis of electromagnetic ion cyclotron (EMIC) wave activity: 24 with prevalent EMIC waves and 24 with no EMIC waves observed on the orbit. There is a close correlation between EMIC waves and perpendicularly heated ion distributions. For protons the perpendicular temperature increase is modest, about 5 eV, and is always observed at 90¿ pitch angles. This is consistent with a nonresonant interaction near the equator. By contrast, He+ temperatures during EMIC wave events averaged 35 eV and sometimes exceeded 100 eV, indicating stronger interaction with the waves. Furthermore, heated He+ ions have X-type distributions with maximum fluxes occurring at pitch angles intermediate between field-aligned and perpendicular directions. The X-type He+ distributions are consistent with a gyroresonant interaction off the equator. The concentration of He+ relative to H+ is found to correlate with EMIC wave activity, but it is suggested that the preferential heating of He+ accounts for the apparent increase in relative He+ concentration by increasing the proportion of He+ detected by the ion instrument. ¿ American Geophysical Union 1994