Janet Leigh's agent initially rejected her participation in this film due to the low salary offered without even consulting the actress. Orson Welles, anticipating this, sent a personal letter to the actress, telling her how much he looked forward to their working together. Leigh, furious, confronted her agent telling him that getting directed by Welles was more important than any paycheck.
Oscar winner Mercedes McCambridge only appears in the film because she was having lunch with Orson Welles during filming and Welles convinced her to film a scene. He had her wear a leather jacket, cut her hair himself and had her character say the sinister line, "I wanna watch."
The opening scene took an entire night to get right, mainly because the actor playing the customs officer kept blowing his lines. It was beginning to get light on the horizon when Orson Welles made the final take of the night, saying to the cast, "All right, let's try it one more time." Then he looked at the actor and said, "If you forget your line this time, just move your lips and we'll dub it in later, but please, God do NOT say, 'I'm sorry, Mr. Welles!'" This is the take seen in the film. However, it is important to add that Welles categorically refused to consider firing this unhappy actor at any point, although Universal executives who were on the set repeatedly urged him to.
Orson Welles said that this was the most fun he'd ever had filming a picture, unlike most of his Hollywood films, because he wasn't troubled by studio interference (until after he completed the picture, anyway). He was given a healthy budget, and he was working with some of his favorite actors on a script that didn't involve as much symbolism and all-out cinematic trickery as something like Citizen Kane (1941).
When Orson Welles discovered that his film was recut, he wrote a letter to the production house with specifics on how he would have wanted the film to be released. This memo, thought to be lost, was found to be in the possession of star Charlton Heston and was the basis for the re-edited 1998 re-release.