Abstract The absorption of electromagnetic radiation by a thin isotropic metal film is expected to become resonant for two equidistant sets of frequencies as a result of the size quantization. The amplitudes of these resonances are shown to be comparable to the background absorption for values of the film thickness up to about 1500 Å if the film is sufficiently pure (relaxation time ф≳10 −11 s ). Effects which are due to static magnetic fields are investigated. If perpendicular to th surface, the field causes a shift of the resonant frequencies by an amount ω c, provided the electromagnetic field is circularly polarized (ω c is the cyclotron frequency). The frequencies increase monotonically with a weak applied magnetic field B parallel to the surface, and become proportional to B 2 3 for larger values of B.