The independent determination of the thicknesses of thin vacuum-deposited metal-films by the method of Tolansky and a X-ray-fluorescence-analytical method showed, that the Tolansky-method generally yields thicknesses, systematically too large by about 60-100 Å. The reason for this discrepancy may be, that the silverfilm, deposited on the testlayer, only incompletely adjusts itself to the roughness of the testlayer-surface. © 1969 Springer-Verlag.