in vivo

In vivo describes biological processes or experiments that occur within a living organism, as opposed to in a test tube or artificial environment.

The Latin phrase literally means "in the living." Scientists distinguish between in vivo studies, which observe phenomena in whole animals or humans, and in vitro studies, conducted in isolated cells or tissues.

The drug showed promise in vitro but failed in vivo trials.

In vivo testing remains essential for understanding how treatments behave in complex living systems.