Working with low voltage microscope (R.C.A., EMC-2, of 30KV.) the authors verified that parlodion and Formvar films are quickly destroyed by intense heating under the electron beam. They have tried to employ oxide films, as Al2O3 and SiO, more resistant to heat. Al2O3 films are prepared by anodic oxidation of thin aluminium sheets, under 8 to 10 volts in a 3% ammonium citrate solution and subsequent aluminium dissolution in a O.25% HgCl2 solution. These films are very suitable when prepared with highly pure aluminium of extremely homogeneous surface. Best results were obtained with SiO films, evaporated in high vacuum over Parlodion films mounted on metallic grids. Employing 1 or 1.5 mg of SiOm highly homogeneous and resistant films are obtained, having little inferior transparence than the Parlodion ones. Pure SiO films (1.5 mg) are obtained by elimination of the Parlodion under slow heating until 250°C; they are greatly transparent but little resistant to water, thus beeing indicated in dry preparations. For particles which deposite in a chain-like form around thin fibers, the authors employ the mounting on Parlodion fibers, obtained by heating Parlodion films on microscope grids about 190°C.