Under mechanical milling (MM) in a planetary ball mill the FeSn intermetallic decomposes with the formation of the Fe5Sn3 and FeSn2 phases, and the Fe2Ge3 decomposes into FeGe (B20) and FeGe2. These processes were investigated using X-ray diffraction (XRD), and magnetization measurements in order to assess whether or not local melting upon impact by milling balls, or low-temperature solid-state processes are responsible for decomposition. Fe2Ge3 decomposes completely after a relatively short milling period, while the amount FeSn decomposed reaches a steady state, depending on milling conditions, after prolonged milling. Particle sizes of the decomposition products (Fe5Sn3 and FeGe) determined from the XRD and magnetization data remain approximately constant during MM. These peculiarities are in good accordance with local melting as a mechanism of the mechanical decomposition of FeSn and Fe2Ge3, (C) 2004 Kluwer Academic Publishers.