Narrow-banded ELF waves with frequencies between the local hydrogen and the singly-charged helium gyrofrequencies have been seen in the S3-3 satellite electric field wave data at altitudes between 800 and 8000 km. The waves are generated in or just below the auroral acceleration region by the accelerated electon beam and propagate in the Alfv¿n-ion cyclotron branch of the cold electromagnetic dispersion relation as modified byt the presence of a two ion H+-He+ plasma.