In vitro toxicology - The analysis of the effects of toxic chemicals on cultured bacteria or mammalian cells. In vitro (literally 'in glass' testing methods are employed primarily to identify potentially hazardous chemicals and/or to confirm the lack of certain toxic properties in the early stages of the development of potentially useful new substances such as therapeutic drugs, agricultural chemicals and direct food additives. Most toxicologista believe that in vitro toxicity testing methods can be a useful, time- and cost-effective supplement to toxicology studies in living animals (which are termed "in vivo" or "in life" methods). However, it is generally accepted that the available in vitro tests are not presently adequate to entirely replace animal toxicology tests.