A laser interferometer which utilizes some Zeeman laser properties has been built and operated. The application of an axial magnetic field constrains a two‐mode 633‐nm He&sngbnd;Ne laser to oscillate simultaneously as left‐ and right‐hand circularly polarized modes at the upper and lower cavity resonances, respectively. The two modes, separated by a quarter‐wave plate and polarizers, are sent through different arms of an interferometer, and are recombined and detected with a photomultiplier. Target motions in one arm, ranging from displacements of 10−6cm at 12 kHz to 10 cm at 0.5 Hz, produced easily resolvable signals in this heterodyne device.