The purpose of any specimen preparation technique is to prepare a sample of material ‘fixed’ in some way as near as possible to its native state, so that its structure has not changed significantly by the time the specimen is examined in the electron microscope, stained if necessary so that it gives adequate contrast, and, in some cases, additionally stained or labelled so that some chemically distinct part of the structure can be identified. Now, these techniques cover an enormous field of work, and at a relatively short meeting like this, one has to select some particular aspects of it. The subject-matter of section II is especially concerned with techniques which involve physical rather than chemical processing of the specimen, and in particular ones which are still only in rather restricted use.