A procedure performed in vitro () is performed not in a living organism but in a controlled environment, such as in a test tube or Petri dish. Many experiments in cellular biology are conducted outside of organisms or cells; because the test conditions may not correspond to the conditions inside of the organism, this may lead to results that do not correspond to the situation that arises in a living organism. Consequently, such experimental results are often annotated with in vitro , in contradistinction with in vivo.

This type of research aims at describing the effects of an experimental variable on a subset of an organism's constituent parts. It tends to focus on organs , tissues , cells , cellular components, proteins, and/or biomolecules. In vitro research is better suited than in vivo research for deducing biological mechanisms of action. With fewer variables and perceptually amplified reactions to subtle causes, results are generally more discernible.

The massive adoption of low-cost in vitro molecular biology techniques has caused a shift away from in vivo research which is more idiosyncratic and expensive in comparison to its molecular counterpart. Currently, in vitro research is vital and highly productive.

However, the controlled conditions present in the in vitro system differ significantly from those in vivo , and may give misleading results. Therefore, in vitro studies are usually followed by in vivo studies. Examples include:

• In biochemistry, non-physiological stoichiometric concentration may result in enzymatic active in a reverse direction, for example several enzymes in the Krebs cycle may appear to have incorrect nomenclature.

• DNA may adopt other configurations, such as A-DNA.

• Protein folding may differ as in a cell there is a high density of other protein and there are systems to aid in the folding, while in vitro, conditions are less clustered and not aided.

It should be pointed out that the term is historical, as currently most lab ware is disposable and made out of polypropylene (sterilizable by autoclaving, ex: microcentrifuge tubes) or clear polystyrene (ex: serological pipettes) rather than glass to ease labwork, ensure sterility, and minimize the possibility of cuts from broken glass.

• Animal testing

• Ex vivo

• In situ

• In utero

• In vivo

• In silico

• In papyro

• In vitro fertilization

• In Vitro Cellular & Developmental Biology - Animal

• In Vitro Cellular & Developmental Biology - Plant