Theoretical and experimental results are presented for the conductance peaks at the cyclotron harmonics in a plasma‐filled cylindrical capacitor. A theory is developed and is shown to predict peak height variation with density, harmonic number, and sheath thickness that is in agreement with experimental observation. A harmonic conductance peak is found to rise initially as density increases, only to fall to a minimum height as the upper hybrid frequency passes through that harmonic. Possible applications of this work to plasma diagnostics and further research are mentioned.