A new method of measuring diffusion in metals with the aid of the microhardness tester according to Hanemann is indicated, taking as an example the diffusion of copper in aluminum. The dependence of the microhardness on the concentration of homogeneous mixed crystals serves as the calibration curve. Microhardness impressions are made in the diffused junction, and these, with the help of the calibration curve, make it possible to determine the concentration.