Different preparative techniques described in the literature were compared for the study of the ventricular surfaces. To develop a standard method applicable also under experimental conditions the following procedure is recommended for scanning electron microscopy. (1) Fixation. After perfusion with a heparin-containing mammalian Ringer-solution (37 degrees C) fixation by collidine-buffered OsO4 (2%). The rate of perfusion should vary between 60--90 drops per minute. Osmotic pressure of the fixative solutions is optimal between 800--1000 mOsm. (2) Drying, Distortion-free drying of the surfaces of the cerebral ventricles cannot be achieved in air. Use of critical point dryers only ensures preservation of the fine structure. (3) Evaporation. The method of metal evaporation is an important part in the development of the final quality of the picture. Distribution of the metal layer is ideal with an Au--Pd alloy. If a rotating metal evaporator is not available, evaporation from different directions also gives satisfactory results.