The negative staining of virus particles for TEM study was introduced in the late 1950s, following the establishment of a standardized procedure by Brenner and Horne in 1959 (1). Rapidly, this staining technique was applied to other biological particulates, usually when a purified or semipurified aqueous suspension of freely suspended (i.e., nonaggregated) material was available. In addition to viruses, this material ranged from purified enzymes and other soluble protein molecules and components of molecular mass in the range of 200 kDa up to several MDa (such as the molluscan hemocyanins and ribosomes), to isolated cellular organelles, membrane fractions, bacterial cell walls and membranes, and filamenous protein structures of many types, also liposomal and reconstituted membrane systems, and even synthetic polymers.