Specimen preparation for transmission electron microscopy starts with the fixation of the specimens with aldehydes and osmium tetroxide. These steps are followed by a gradually dehydration of the specimens with organic solvents and a subsequent infiltration of the specimens with resin. The resin must polymerize prior to ultramicrotomy. During this process the specimens are cut into thin slices of 50 – 70 nm and then transferred to a grid. After staining of the ultrathin sections with uranyl acetate and lead citrate the specimens can be examined with a transmission electron microscope.