Using transmission electron microscopy we have studied the influence of the electron beam in an electron microscope onto platinum clusters deposited on a thin single crystalline gamma-Al2O3 film grown by oxidation of NiAl(110). At electron current densities below j approximate to 1 A/cm(2) no influence is observed. Movement and coalescence of clusters occur at electron beam current densities between j = 2 and some 10 A/cm(2). For current densities around j = 50 A/cm2 decoration of steps takes place. Further increase to j = 100 A/cm(2) and above induces drilling of holes into the substrate by clusters. At such current densities also melting of the clusters may occur. Due to the heat capacity of the system the result does not only depend on the electron current density but also on the irradiation time.