Two borehole instrumentation systems for the measurement of complex propagation constant in the frequency range from 300 kHz to 25 MHz are described. The first system measures the ratio of the signals coupled to two identical receivers in separate boreholes at different ranges from an isolated transmitter in a third borehole. The second system operates in a single borehole by measuring the mutual impedance between two magnetic dipoles aligned parallel to the borehole. This second system has an automatic digital data acquisition system based on a programmable calculator which reduces the data to conductivity and dielectric constant versus frequency. Examples of data on conductivity and permittivity of actual boreholes in various geologic materials are given.