An analysis is given of the x‐ray diffraction line broadening caused by concentration variations occurring within coherently diffracting crystallites. The sine Fourier coefficients of the line profile are employed. The method is applied to sintered and unsintered AuPt alloy catalysts. In the interior of the crystallites of the sintered specimen, the concentration maintained a constant value which agreed very well with the average composition. The surface region was enriched by gold, in agreement with experimental results from other methods and with theoretical predictions. Concentration variations in the unsintered specimen were much larger. The crystallites consisted of a platinum‐rich nucleus surrounded by a gold‐rich shell as may be expected from the preparation method (chemical reduction of platinum and gold ions in solution). In addition, a method for correction of the ’’hook’’ effect in line profile analysis is suggested.