We present theoretical and experimental results relevant to azimuthal magnetoplasma sheath waves in the case of the magnetic field parallel to the axis of a thick conducting cylinder. For the theory, a planar geometry is used with the ambient magnetic field parallel to the conducting plane and propagation perpendicular to the magnetic field. The results show two low-frequency transverse magnetic (TM) modes propagating in opposite directions with different propagation constants and also different cutoff frequencies separated by the cyclotron frequency. At frequencies above the upper hybrid frequency, one unidirectional TM mode is found. No transverse electric (TE) modes have been found. The experimental setup consists of a metallic cylinder with two protruding radial monopole antennas separated by an angle of 90¿, placed in an axially magnetized laboratory plasma. Measurements of the two-port S parameters clearly show nonreciprocity caused by the propagation of different wave modes in opposite directions. ¿ American Geophysical Union 1996