Abstract
We show how the Zeeman pattern of the "satellites" of spectral lines produced by the high-frequency Stark effect can be used to determine the direction of an oscillating electric field relative to the magnetic field. We illustrate the use of this effect as a diagnostic technique in plasma physics by observations of the Zeeman pattern of the "plasma satellites" of the 4922-Å He-I line produced by high-frequency electric fields in a beam-plasma interaction.