We present spectral generalized magneto-optical ellipsometry as an optical tool to investigate magnetic and electronic properties of ferromagnetic materials. The advantage of the simultaneous observation of the dielectric and the magnetic responses within one measurement procedure is crucial for materials with coupled degrees of freedom near a phase transition or during annealing procedures to improve the film quality by removing grain boundaries. Moreover, we show the implementation of this technique within an UHV-cryostat for a temperature range between 4.2 and 800 K and fields up to 40 mT. Examplary measurements on iron and Permalloy demonstrate the comfortable application of this technique. (C) 2003 Elsevier B.V. All rights reserved.