Abstract: A measurement method and an apparatus are used for determining the moisture content of sheet- or foil-like materials (1) of high moisture content and low electrical conductivity. Ground planes (3) are adapted on both sides of the material (1) to be measured; between each ground plane (3) and the material (1) to be measured, at least one center conductor (2) is adapted approximately parallel to the material (1) to be measured in order to form a quasi-TEM transmission line resonator. Electromagnetic RF energy is fed into the quasi-TEM transmission line resonator so that the electromagnetic quasi-TEM waves propagate in the plane of the material (1) to be measured. The resonator supports for the transverse and longitudinal waves such resonant modes whose resonant frequencies and Q's are dependent on the properties of the material (1) to be measured.