He was a doctor at the Auschwitz extermination camp. He was appointed chief doctor by Himmler. He joined other doctors (such as Koenig, Thilon, and Klein) in the task of choosing employable Jews to operate the industrial machines and sending others to the gas chambers. The selection was mostly haphazard. The inmates were paraded before Mengele, who called either "Right!" (to the work squads) or "Left!" (to the gas chambers). He promoted medical experimentation on inmates, and he took an especial interest in dwarves and twins. He supervised an operaiton by which two Gypsy children were sewn together to create artificial conjoined twins. The medical tools employed in the operation were dirty, and the children soon acquired an infection where their veins had been resected. They died of gangrene two weeks later.

Witnesses at the Frankfurt Trial told of his standing before his victims with his thumb in his pistol belt and choosing candidates for the gas chambers. When it was reported that one block was infected with lice, he solved the problem by gassing all of the 750 women assigned to it.

The only firsthand evidence on these experiments comes from a handful of survivors and from a Jewish doctor, Miklo Nysizli, who worked under Mengele as a pathologist. Mengele subjected his victims - twins and dwarves aged two and above - to clinical examinations, blood tests, X-rays, and anthropological measurements. In the case of the twins, he drew sketches of each twin, for comparison, He also injected his victims with various substances, dripping chemicals into their eyes (apparently in an attempt to change their color).

He then killed them himself by injecting chloroform into their hearts, so as to carry out comparative pathological examinations of their internal organs. Mengele's purpose, according to Dr. Nyiszli, was to establish the genetic cause for the birth of twins, in order to facilitate the formulation of a program for doubling the birth rate of the "Aryan" race. The experiments on twins affected 180 persons, adults and children.

Mengele also carried out a large number of experiments in the field of contagious diseases, (typhoid and tuberculosis) to find out how human beings of different races withstood these diseases. He used Gypsy twins for this purpose. Mengele's experiments combined scientific (perhaps even important) research with the racist and ideological aims fo the Nazi regime, which made use of government offices, scientific institutions, and concentration camps.

From the scanty information available, it appears that his research differed from the other medical experiments in that the victims' deaths were programmed into his experiments and formed a central element in them.

Himmler, writing to SS-Oberführer Brack, on August 11, 1942, expressed an interest in sterilization experiments involving the use of x-rays (See auschwitz sterilization). In April of 1944, he received a report of the work of Dr. Horst Schumann "on the influence of X-rays on human genital glands" at Auschwitz. The report included the following statement:

"Previously you have asked Oberführer Brack to perform this work, and you supported it by providing the adequate material in the concentration camp Auschwitz. I point especially to the second part of this work, which shows that by those means castration of males is almost impossible or requires an effort which does not pay. As I have convinced myself, operative castration requires not more than 6 to 7 minutes, and therefore can be performed more reliably and quicker than castration by X-rays."

Schumann set up an X ray station at Auschwitz in 1942, in the woman's camp Bla. Here men and women were forcibly sterilized by being positioned repeatedly for several minutes between two x-ray machines, the rays aiming at their sexual organs. Most subjects died after great suffering, or were gassed immediately because the radiation burns from which they suffered rendered them unfit for work. Men's testicles were removed and sent to Breslau for histopathological examination.

The frequently following ovariotomies were performed also by the Polish prisoner, Dr. Wladyslav Dering. Dering once bet with an SS man that he could perform ten ovariotomies in an afternoon, and won his bet. Some of his victims survived. Dering was declared a war criminal but eluded justice and for a time practiced medicine in British Somaliland.

Dr. Herta Oberhauser killed prisoners with oil and evipan injections, removed their limbs and vital organs, rubbed ground glass and sawdust into wounds. She drew a twenty-year sentence as a war criminal, but was released in 1952 and became a family doctor at Stocksee in Germany. Her license to practice medicine was revoked in 1960.

Professor Carl Clauberg performed experiments into sterilization at both Auschwitz and Ravensbrück. This was done on Hitler's initiative, as he had been convinced by several doctors that mass sterilization could provide a powerful weapon against Germany's enemies during total war.

Clauberg injected chemical substances into wombs during normal gynocological examinations. Thousands of Jewish and Gypsy women were subjected to this treatment. Clauberg sought to answer Himmler's query about how long it would take to sterilize one thousand women, and eventually informed him that, using methods he developed, a staff of one doctor and ten assistants could do the job in a single day. The injections totally destroyed the lining membrane of the womb and seriously damaged the ovaries of the victims, which were then removed and sent to Berlin to test the effectiveness of the method.

After Ravensbruck, she was the head of the women's camp at Auschwitz; the prisoners referred to her as 'the beast.' For her share in the selections for the gas chambers and medical experiments and for her torture of countless prisoners, she was condemned to death in 1947 as a war criminal.

As an empolyee of IG-Farben and Leverkusen, he carried out medical experiments with different sorts of medicine at KZ Gusen. He specialized in tuberculosis and experimented in 1944 with "Ruthenol" and "Praeparat 3582" at Block No. 27 of KZ Gusen I. These were similar to his experiments at KZ Auschwitz.

Besides his private experiments, he specialized in the production of preparations of human heads. Some of these preparations were shown in the KZ Gusen Pathological Museum. The others were sent to friends of Dr. Herbert Heim as special gifts, or were used by Heim as weights on writing desks.

Between October, 1941, and autumn of 1943, he was Chief-Physician of the SS and the Police at Linz, Steyr, Wels and KZ Mauthausen-Gusen. He was the first to start mass-execution of ill and unfit prisoners by heart injections. So he was nicknamed "Dr. Spritzbach" (Injection Doctor) in the camps. In January of 1942, 732 Spanish inmates and 571 Soviet inmates were exterminated by heart injections at KZ Gusen Concentration Camp. In genereal, heart injections were given at KZ Gusen Camp two times a week until April of 1945. The career of Dr. Krebsbach ended at KZ Mauthausen-Gusen when he shot Josef Breitenfellner, a young man from Langenstein-Village who served in the German Army at that time and was home for vacation. Due to this crime, Dr. Krebsbach was moved from KZ Mauthausen-Gusen to KZ Warwara, where he led the selections along with the liquidation of that camp in August of 1944. Later, he worked as the Inspector for Epidemies in the occupied countires of Lettland, Estland and Lithuania. The following SS Doctors refused to give heart injections at KZ Gusen: