According to Alfred Hitchcock, this was another of his experimental movies. In addition to the dialogue, the plot is revealed through the use of colors, predominantly red, yellow and white. He admits that this did not work out.
Alfred Hitchcock hired Leon Uris to adapt his own novel. But Uris didn't care for Hitchcock's eccentric sense of humor, nor did he appreciate the director's habit of monopolizing all of his time as they worked through a script. Hitchcock was disappointed that Uris seemed to ignore his requests to humanize the story's villains. In his opinion the novel painted them as cardboard monsters. With only a partial draft completed, Uris left the film.
Leon Uris wrote the first draft of the screenplay, but Alfred Hitchcock declared it unshootable at the last minute and called in Samuel A. Taylor (writer of Vertigo (1958)) to rewrite it from scratch. Some scenes were written just hours before they were shot.
An early scene is portrayed in a department store "Den Permanente". In Torn Curtain (1966), there is a poster for this same store, displayed when Julie Andrews climbs to the top of the stairs to enter the bookstore.
This was the second appearance of Karin Dor in an English-language feature but the first time her own voice was kept in the original version. She has appeared in You Only Live Twice (1967) two years before but was dubbed by another English actress then.
The shop that the Kusenovs visit just before their defection is Den Permanente, a permanent exhibition of Danish Arts and Crafts. It was founded in 1931 as a cooperative by some Danish artists and craftsmen.
After Leon Uris left the film, Alfred Hitchcock asked Arthur Laurents if he was interested in working with Hitchcock on the script of Topaz. But Arthur Laurents refused. So Hitchcock called Samuel A. Taylor to work on the script. One of the difficulties Hitchcock and Samuel Taylor faced was they didn't have enough time to work on the script. According to the book "The A-Z of Hitchcock", Samuel Taylor had to continue writing throughout the shooting.
The opening credits lists the most comprehensive cast - all 25 members; the end credits list only 11 of those members with character names. IMDb policy, therefore, requires the opening cast list to be used.
The trivia items below may give away important plot points.
The duel ending for Topaz (1969) was the original ending of Topaz (1969). According to the Book "Alfred Hitchcock: A Life In Darkness And Light" Pg. 692, "after finishing principal photography in March, the director took a short break, then returned in Paris in mid-April to shoot the grand climax of the film. This was to be the greatest of film's choreographed crescendos - a scene not in the book, but in Hitchcock's mind from the beginning. It was an old-fashioned pistol duel between Devereaux (Stafford) and Granville (Piccoli), the "topaz" mole and lover of Madame Devereaux, set at dawn in a deserted soccer stadium." But halfway through the week-long shot, Hitchcock had to leave when he heard that his wife Alma had been hospitalized. Before he left for Hollywood, Hitchcock gave Herbert Coleman precise instructions on how to shoot the rest of the scenes in the duel ending. But the editing of the duel sequence ended up becoming a particular sore point.