A nondestructive method for determining the thickness of a metallic protective layer determined by detection of a different type of intervening layer which is situated between the metallic protective layer and the metallic base material, by ultrasound, eddy-current or (pulsed) thermography. The intervening layer may comprise a nonmetallic layer of oxides or carbides, a metallic layer of pure nickel or a layer with depleted Al and Ti content in that region of the base material which is close to the surface. This method can be used for turbine blades in order to determine the layer thickness, for example during the test phase of coating, and to avoid the known destruction of the turbine blade, which is labor- and cost-intensive.