After being arrested, along with two of his sons, on the night of the German invasion of Austria, March 11, 1938, Loewi was released on condition that he "voluntarily" relinquish all his possessions, including his research, to the Nazis. Loewi moved to the United States in 1940, where he became a research professor at the New York University College of Medicine. In 1946, he became a naturalized citizen of the United States. In 1954, he became a Foreign Member of the Royal Society. He died in New York City on December 25, 1961.