The quantity of pharmaceutical and cosmetic products with different composition and the diversity of contaminating microorganisms set up special problems for each product with its specific field of application. It is not exact to generalize the hazard of contaminating microorganisms to product cathegories. Some product cathegories however are more imperilled to be contaminated with microorganisms and they are more hazardous than other ones. The most important component of the living matter is water that decides on growth, multiplication and survival of microorganisms in drugs and cosmetics. Products with a high content of available water are the most problematic ones. The consequences of survival and multiplication of microorganisms in relation to metabolic activity, pathogenicity and route of administration can be harmless or fatal. The nutritive wants of many microorganisms are very small, even simple salt solutions do not exclude microbial growth. There scarcely exist substrates not used as energy source by any microorganism and so it does not wonder that desinfectants are also used. Added preservatives may be absorbed or inactivated by suspended anorganic components, swelling agents, solubilizers etc., the containers or its closing. In the water phase of emulsions, in which under special conditions smaller amounts of the preservative are available, microorganisms sometimes can multiply. Skin care products neither belonging to pharmaceuticals nor to cosmetics present special clinical problems. Many times creams and lotions contain ingredients metabolized by microorganisms. Ointments and oils can be overgrown only by highly specialized organisms but if there is condensed water as a film at boundary surfaces much more microorganism species can grow. When using cosmetics it must be considered that parts of them will get into the eye. The eye is really endangered by Pseudomonads, which can according to the composition multiply in shampoos and whose contact to the eye can not be excluded. Syrups and solutions contain sugar concentrations, which suppress growth of most microorganisms except osmotolerant germs. Because of their low water content powders normally are protected against microbial growth but they should be free from clostridial spores for a mixture of powder and sweat is a good nutrient medium to Clostridia and fungi. Powders for surgical use must be sterile. Tablets and dragees do not allow microbial multiplication because of their low water activity. Under bad storage conditions a local increase of water content may permit microbial growth at the surface, especially in hygroscopicity. Fortunately there is seen a trend of not using multi-dose-containers for injections because of the high risk of contamination. It is to develop single-dose-containers also for other groups of preparations especially for eye-preparations. Many products microbiologically unobjectionable produced are contaminated in use, they contain the spectrum of microorganisms of the area of application...