Complex resistivity may provide valuable information about the structural and hydraulic nature of porous media and fluids contained within such media. The environmental value of such a property is obvious. To date most environmental applications of complex resistivity have focussed on relatively crude data analysis methods and restrictive electrode configurations. New tomographic methods are becoming available that will allow complex resistivity to be employed with arbitrary electrode arrangements. Laboratory trials of our extensions of electrical resistivity tomography to a complex form are reported. The inversion procedure is presented and demonstrated for a range of targets, with resistive and reactive characteristics. The approach is shown to provide useful magnitude and phase images, giving spectral information about the region of interest. Cole–Cole analysis of the inversion results reveals specific material relaxation characteristics. The usefulness of imaging complex resistivity is evident when compared with more conventional resistivity tomography, in particular when examined over a range of input frequencies.