Motivazioni dell’agire dei medici che hanno applicato l’eutanasia nel regime nazi-fascista - Michael von Cranach in this paper reports the killing of hundreds of thousands of disabled persons, mentally or physically ill, slaughtered in gas chambers or given lethal drugs, in the Third Reich during the Nazi period. The genocide of helpless and ailing persons (in addition to that of Jews, Gypsies and homosexuals) put into operation under the principles of eugenics, defence and health of the Arian race. In reality, the genocide represented a sadistic exercise of power, that alleged itself the right to decide on citizens’ life or death. Many physicians connived with the regime and were consequently considered the progressive élite of the medical profession. Keywords: eugenics, defence of the race, biopolitics, exercise of power, scientific and progressive medicine under the Third Reich.