Six years after it was first introduced into psychiatry in 1938, electro-convulsive therapy (ECT) became the subject of criminal human experiments in Nazi Germany. In 1944, at the Auschwitz III / Monowitz camp hospital, the Polish Jewish prisoner psychiatrist Zenon Drohocki started experimental treatments on prisoners with an ECT device that he had constructed himself. According to eyewit-nesses, Drohocki’s intention to treat mentally unstable prisoners was soon turned into something much more nefarious by SS doctors (including Josef Mengele), who used the device for deadly experiments. This article provides an account of this important and little-known aspect of the early history of ECT, drawing on an extensive array of historical literature, testimonies, and newly accessible docu-ments. The adoption of ECT in Auschwitz is a prime example of the “grey zone” in which prisoner doctors had to operate—they could only survive as long as the SS considered their work useful for their own destructive purposes.