Bernard Herrmann wrote the original score, but Universal Pictures executives convinced Hitchcock that they needed a more upbeat score. Hitchcock and Herrmann had a major disagreement, the score was dropped and they never worked together again.
Alfred Hitchcock originally wanted to cast Cary Grant in the lead role, but Grant told him he was too old.
A scene showing actor Wolfgang Kieling, who played Gromek, also playing Gromek's brother was cut. In it he shows Michael Armstrong (Paul Newman), who has just killed Gromek, a picture of Gromek's three children. It was believed that this would have shifted the audience's sympathy away from Newman to the dead man. Unfortunately, a close-up of the brother cutting a sausage with a knife similar to the one used in the murder, a characteristically Hitchcockian shot, was also lost.
According to Norman Lloyd, Universal wanted Henry Mancini to do the score, so they pressured Alfred Hitchcock not to hire 'Bernard Herrmann'.
According to the book "Hitch: The Life and Times of Alfred Hitchcock", Hitchcock was unsatisfied with Brian Moore's Screenplay. So Hitchcock brought in Keith Waterhouse and Willis Hall to do a rewrite job on it. Their contribution to the Screenplay was considerable enough for Hitchcock to feel strongly that they should receive screen credit. But Brian Moore disputed this, and an adjudication by the Screenwriters Guild gave him sole credit, to Hitchcock's irritation.
According to the book "It's Only a Movie", Brian Moore was chosen to write the screenplay, but shooting began before Hitchcock was satisfied with the script, dictated by the limited availability of Julie Andrews.
According to the book "It's Only a Movie", Hitchcock said: "THERE WAS AN ENDING written which wasn't used, but I rather liked it. No one agreed with me except my colleague at home his wife Alma Reville. Everyone told me that you couldn't have a letdown ending after all that. Paul Newman would have thrown the formula away. After what he has gone through, after everything we have endured with him, he just tosses it. It speaks to the futility of all, and it's in keeping with the kind of naivete of the character, who is no professional spy and who will certainly retire from that nefarious business."
According to Truffaut/Hitchcock Interview, Alfred Hitchcock told Truffaut that he is giving "Gromek's brother" scenes to Truffaut. Truffaut told Hitchcock that he will look at these scenes and then turn them over to Henri Langlois for the Cinematheque Francaise. But it has yet to be found and is generally considered to be lost.
Hitchcock wanted to cast Eva Marie Saint, whom he had previously directed in North by Northwest. However, the studio felt that, at 42, Saint was too old to play the female lead. They instead cast the younger and more popular Julie Andrews.
In the shot in which Alfred Hitchcock's cameo occurs, the music briefly changes to "Funeral March of a Marionette" by Charles Gounod, which is best known as the main theme for Alfred Hitchcock Presents.
One of the reasons Alfred Hitchcock did not want to use Paul Newman and Julie Andrews was their very high fees.For the rest of his career Hitchcock would never hire performers with the same sort of fee or above.
The opening credits lists the most comprehensive cast - all 14 members; the end credits lists only 12 of those members with character names. IMDb policy, therefore, requires the opening cast list to be used.
The scene where Gromek is killed was written to show how difficult it really can be to kill a man.
The Scenes with Gromek's older brother was originally part of the final cut. Wolfgang Kieling (Gromek in this film) wrote in his autobiography that it was Paul Newman who wanted Gromek's older brother scenes to be removed from the final cut. Wolfgang Kieling also played Gromek's older brother. Bernard Herrmann composed 2 cues for Gromek's brother scenes. They are called "Photos" and "Sausage."
The Swedish actor Jan Malmsjö (who had a small uncredited role as photographer in the final scenes in Helsingborg harbour and customs) found that a lot of signs were not written in correct Swedish so he helped the film crew to correct them.
Was reportedly one of Alfred Hitchcock's most unhappy directing jobs.
Alfred Hitchcock:
early in the film sitting in a hotel lobby with a baby on his knee. He transfers the baby to his other knee, and then rubs his knee, as if disdainfully looking at something the baby has done to it.