He then studied medicine at the universities of Freiburg, Kiel, Greifswald, Graz and finally Würzburg, where he received his doctorate in 1923 with the dissertation Über einen Fall von präsystolischem Galopprhythmus mit gleichzeitigem 'Flint'schen Geräusch' bei einer Aorteninsuffizienz (On a case of presystolic gallop rhythm with simultaneous 'Flint'schen noise' in an aortic insufficiency).
Holzlöhner was a private lecturer and senior physician with Wilhelm Trendelenburg at the Physiological Institute of the University of Berlin.
Together with his assistants Sigmund Rascher and Erich Finke, he carried out sub-cooling experiments on behalf of the Luftwaffe in the Dachau concentration camp from August 1942, in which prisoners were deliberately chilled, i.e. by immersing prisoners in tanks of ice water to simulate hypothermia, then reheated using different methods.
[1] At the conference on medical questions in distress and winter death on October 26 and 27, 1942, he discussed the results of the cold tests.
A photograph of Rascher and Holzlöhner appeared in Life in a feature on the Nuremberg medical tribunal with the caption 'Human Laboratory Animals'.