In vitro, in vivo, in silico: what the research terms mean
What in vitro, in vivo and in silico mean in research, how in vitro and in vivo work differ, and how the terms relate to research-use-only reagents.
By Zachery Casey · Published · Reviewed · Editorial policy
In vitro means outside a living organism, in a tube or dish; in vivo means within a living organism; in silico means on a computer. Research papers, product labels and supplier pages use these Latin phrases to say where an experiment happens, and "in silico" has joined the older two as more work moves onto computers. This guide explains what each term means, how they differ, and how they connect to the "research use only" label on laboratory reagents.
Terms are defined in the glossary.
The terms at a glance
| Term | Latin meaning | Where the work happens |
|---|---|---|
| In vitro | "In glass" | In a test tube, plate, flask or instrument, outside a living organism |
| In vivo | "In the living" | Within a whole, living organism |
| Ex vivo | "Out of the living" | In tissue taken from an organism and studied outside it |
| In situ | "In its place" | Where something naturally occurs, without moving it |
| In silico | "In silicon" | On a computer, by modelling or simulation |
"In silico" is modern dog Latin, modelled on the older terms. Silicon refers to the computer chip.
What is in vitro?
"In vitro" is Latin for "in glass", from the glassware where such work was first done. Today the vessel is as likely to be plastic, but the meaning is the same: the work takes place in a controlled, artificial setting rather than inside a living organism.
In vitro work covers a wide range:
- Analytical chemistry: measuring purity by HPLC, confirming identity by mass spectrometry, or measuring concentration by UV absorbance.
- Biochemical assays: studying how a purified enzyme or protein behaves in a buffer.
- Cell culture: growing cells in dishes or flasks, under aseptic technique. Reagents for cell assays are often checked for endotoxin, a bacterial contaminant.
- Structural studies: methods such as NMR, FTIR and X-ray crystallography.
The main strength of in vitro work is control. The researcher sets the temperature, the buffer and pH, the concentrations and the timing, and can repeat the experiment exactly. Its main limit is that an artificial setting is simpler than a living system, so a result in a tube doesn't automatically carry over to anything more complex.
What is in vivo?
"In vivo" is Latin for "in the living". It describes research carried out within a whole, living organism, with all its systems working together. In vivo studies are a separate field with their own regulation, ethics approval and licensing, and they sit outside anything this library covers.
In vitro vs in vivo
| In vitro | In vivo | |
|---|---|---|
| Setting | Artificial and controlled | A whole, living organism |
| Variables | Few, set by the researcher | Many, interacting |
| Repeatability | High | Lower, because organisms vary |
| Speed and cost | Usually faster and cheaper | Usually slower and dearer |
| What it shows | How something behaves under defined conditions | How something behaves within a complete living system |
The two answer different questions. In vitro work is usually done first, because it is quicker, cheaper and easier to interpret.
Ex vivo and in situ
Ex vivo work uses tissue or cells taken from an organism and studied outside it for a short time, before they change much. It sits between in vitro and in vivo.
In situ means "in its original place". In chemistry and biology it describes measuring or reacting something where it already is, rather than extracting it first. For example, a reagent may be generated in situ in a reaction flask instead of being made separately and added.
What is in silico?
"In silico" describes work done on a computer: modelling, simulation and calculation. Examples include predicting a peptide's molecular weight or isoelectric point from its sequence, modelling how a molecule folds, and searching databases such as PubChem.
In silico results are predictions. They are only as good as the model and data behind them, and they are usually checked by in vitro measurement. A calculated isoelectric point, for example, is a guide for planning rather than a measured property, as the isoelectric point guide explains.
In vitro, research use only and IVD
Two labels on reagents use the same Latin and are easy to confuse:
- Research use only (RUO) means a product is supplied for laboratory research. It is not a medicine, and it is not for diagnostic use. In the US, RUO products must be labelled "For Research Use Only. Not for use in diagnostic procedures." (21 CFR 809.10).
- In vitro diagnostic (IVD) devices are tests regulated for diagnostic use. In Great Britain they are regulated as medical devices. An RUO reagent is not an IVD, and can't be used as one.
For what "research use only" means under UK law, and its limits, see are peptides legal in the UK.
Our products
Our products are chemical reagents for in vitro laboratory work, such as analytical methods and in vitro assays. They are not medicines, they have not been approved by the MHRA or any other regulator, and they are not for human or veterinary use. Every buyer confirms this at checkout. See our research use policy.
Related guides
For what a reagent's lot document shows, see what a certificate of analysis tells you. For the computer tools mentioned above, see lab calculators. Every lot has its own COA, published on the product page and on that lot's own page. See Quality.
More on research basics
- Confidence intervals, standard error and error bars: reading the spread in lab resultsWhat a confidence interval is, how standard error differs from standard deviation, how to work out a 95% interval, and how to read error bars on a graph.
- P-values and statistical significance: comparing two results with a t-testWhat a p-value is and isn't, what statistical significance means, and how a t-test compares two sets of lab results, with a worked HPLC example.
- Looking up a compound: CAS numbers, PubChem and the literatureWhat a CAS number is and how to check one, plus how to identify a research compound with PubChem, UniProt and PubMed, and why salts get their own entries.