The pharmaceutical industry is dependent upon the physiological activity of chemical entities called drugs which may either be derived from natural sources, principally of vegetable origin, or synthesized in the laboratory. The relationship between the dissolution rate and surface area had been established and methods were available in pharmaceutical technology laboratories for particle characterization. Pharmaceutical processing has been considerably involved with fine particles, and the mortar and pestle represents a symbol of pharmaceutical processing which dates back into antiquity. The official methods for characterization of particle size and shape of drugs are quaint by modem standards. The official compendia rely largely on sieving techniques introduced when drugs were derived solely from vegetable sources. The US Pharmacopeia applies a well-defined membrane filtration system to the examination of particulate contamination in single-dose large-volume injection solution. Particle size must be reduced in the preparation of suspensions for injection, simply in order that they may be able to pass through the needle when administered.