Von Euler liked to travel, so he also worked and learned biophysics with Archibald Vivian Hill, again in London in 1934, and neuromuscular transmission with G. L. Brown in 1938.

From 1946 to 1947, he worked with Eduardo Braun-Menéndez in the Instituto de Biología y Medicina Experimental in Buenos Aires, which was founded by Bernardo Houssay.

His unerring instinct to work with important scientific leaders and fields was to be proved by the fact that Dale, Heymans, Hill and Houssay went to receive the Nobel prize in physiology or medicine.

His early collaboration with Liljestrand had led to an important discovery, which was named the Euler–Liljestrand mechanism (a physiological arterial shunt in response to the decrease in local oxygenation of the lungs).

He and his group studied thoroughly its distribution and fate in biological tissues and in the nervous system in physiological and pathological conditions, and found that noradrenaline was produced and stored in nerve synaptic terminals in intracellular vesicles, a key discovery which changed dramatically the course of many researches in the field.