- 'Stewart, James' was very interested in starring in this movie, begging Hitchcock to let him play Thornhill. Hitchcock claimed that Vertigo (1958)'s lack of financial success was because Stewart "looked too old". MGM wanted Gregory Peck, but Hitchcock cast Cary Grant.
- It was journalist Otis L. Guernsey Jr. who suggested to Hitchcock the premise of a man mistaken for a nonexistent secret agent. He was inspired, he said, by a real-life case during WW2 when some secretaries at a British embassy in the Middle East, for fun, invented a nonexistent agent and successfully tricked the Germans into looking for him.
- Hitchcock couldn't get permission to film inside the U.N., so footage was made of the interior of the building using a hidden camera, and the rooms were later recreated on a sound stage.
- The final chase scene was not shot on Mount Rushmore; Hitchcock couldn't gain permission to shoot an attempted murder on a national monument. The scene was shot in the studio on a replica of Mount Rushmore. Everything is shot carefully, so as to avoid associating the faces of the monument with the violence.
- Rather than go to the expense of shooting in a South Dakota woodland, Hitchcock planted 100 ponderosa pines on a MGM soundstage.
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