German physicians and other researchers used the vast concentration camp network as large laboratories, conducting brutal, painful and frequently deadly experiments on the prisoner populations. The forms of experiments varied: from those aiming to aid the military with either weapons development or knowledge creation related to the effects of weapons or battle conditions, to those designed to reinforce Nazi claims of the existence of a racial hierarchy, and experiments that served no other purpose than sadistic torture. The most infamous experiments took place at Sachsenhausen, Dachau, Ravensbrück, Buchenwald, Auschwitz, and Neuengamme, under the direction of physicians Karl Brandt (1904–1948) and Josef Mengele (1911–1979), the latter of whom is known especially for his experiments on twins at Auschwitz. Twenty physicians responsible were prosecuted for crimes against humanity.

This image shows an unconscious prisoner at the Dachau concentration camp who had been subjected to a high-altitude simulation designed to test the limits of human endurance and survival with and without oxygen. The experiment was designed to approximate the conditions a German pilot would face in the event that his aircraft was destroyed at high altitude and had been commissioned by the German air force. The victim was locked in an airtight, low-pressure chamber, after which he was subjected to extreme and rapid changes in pressure. Many perished in the process. The photograph was taken by Sigmund Rascher, an SS physician who carried out particularly dangerous and often deadly medical experiments at Dachau. Heinrich Himmler had ordered that prisoners at Dachau who had been given a life sentence and survived one of these experiments were to be pardoned. Poles and Russians, however, were expressly excluded from this. According to the image caption, the test subject shown here was a Soviet prisoner.
Rascher and his wife were convicted of several other crimes and executed by the SS shortly before the end of the war, so Rascher could not be tried for the crimes against humanity he committed.