in vivo vs. in vitro

in vivo vs. in vitro: What’s the difference?

The scientific terms in vivo and in vitro are used to describe biological processes—specifically, to indicate where a process happens. In vivo (Latin for “in something alive”) means happening inside a person or in a natural setting. In vitro (Latin for “in glass,” as in a glass test tube) means happening in a lab or other controlled environment—not inside a body or natural setting. For example, in vitro fertilization involves fertilization that happens outside the body.