Calculations of the input admittance of a thin cylindrical horizontal dipole antenna over a two‐layered lossy half‐space have been carried out. This has allowed an evaluation to be made of the sensitivity of admittance measurements to variations in the electrical characteristics of the Earth below a conducting overburden and hence to determine the potential of such measurements in geophysical surveying. The results show that maximum sensitivity to changes in the complex permittivity of the lower half‐space is obtained by the use of a band of frequencies about the first antenna resonance. The maximum depth of sensitivity of the observations was found to be approximately one quarter of the resonance wavelength or 8 m for an antenna of length 15 m, indicating that admittance measurements provide a potentially useful and simple geological surveying tech