The heating of heavy ions such as ionospheric oxygen ions in the presence of auroral electrons was studied theoretically and by using numerical simulations. It was found that the ion-ion hybrid mode becomes unstable when the electron drift speed is too small to excite the lower hybrid instability. The linear dispersion relation shows that for electron drift, &OHgr;0&OHgr;H, the lower hybrid mode is excited. Here &OHgr;H and &OHgr;0 are the hydrogen and oxygen gyrofrequencies and v0 is the electron drift speed along the magnetic field lines. The results of the numerical simulations confirm the presence of these two instabilities and show that both light and heavy ions are heated perpendicularly with respect to the magnetic field. In particular, the formation of a high energy tail was observed for heavy ions, and the bulk light ions were heated. ¿American Geophysical Union 1987