Prior to the onset of World War II, Max von Laue and James Franck had sent their gold Nobel Prize medals to Denmark to keep them from being confiscated by the Nazis.  After the Nazi invasion of Denmark this placed them in danger; it was illegal at the time to send gold out of Germany, and were it discovered that Laue and Franck had done so, they could have faced prosecution.  To prevent this, de Hevesy concealed the medals by dissolving them in aqua regia and placing the resulting solution on a shelf in his laboratory at the Niels Bohr Institute in Copenhagen. After the war, he returned to find the solution undisturbed and precipitated the gold out of the acid. The Nobel Society then recast the medals using the recovered gold and returned them to the two laureates.
By 1943, Copenhagen was no longer safe for a Jewish scientist and de Hevesy fled to Sweden, where he worked at the University of Stockholm until 1961. In Stockholm, de Hevesy was received at the department of chemistry by the Swedish professor and Nobel Prize winner Hans von Euler-Chelpin, who remained strongly pro-German throughout the war. Despite this, de Hevesy and von Euler-Chelpin collaborated on many scientific papers during and after the war.
While in Stockholm, de Hevesy received the Nobel Prize in chemistry. He was later inducted into the Royal Swedish Academy of Sciences and received the Copley Medal, of which he was particularly proud. De Hevesy stated: "The public thinks the Nobel Prize in chemistry for the highest honor that a scientist can receive, but it is not so. Forty or fifty have received Nobel chemistry prizes, but there are only ten foreign members of the Royal Swedish Academy, and only two have received a Copley." (Bohr was the other one.)  He received the Atoms for Peace Award in 1958 for his peaceful use of radioactive isotopes.