- Career Resurrection: Alfred Hitchcock's last real hit had been The Birds, and his subsequent films failed to click with either filmgoers or critics, but Frenzy was regarded as a return-to-form that showed that the septuagenarian director still had some relevance. It made back almost six times its budget at the box office and landed on several critics' year-end Top 10 lists
- Deleted Role: Margaret Nolan appeared as one of Rusk's potential victims, though her footage was cut from the film.
- Disowned Adaptation: Novelist Arthur La Bern later expressed his dissatisfaction with Anthony Shaffer's adaptation of his book.Bern: I endured 116 minutes of it at a press showing and it was, at least to me, a most painful experience.
- Wag the Director: Having lived outside of England for so long, Hitchcock had outdated notions about British culture, and several of the cast were unhappy with the lack of authenticity and Britishness of some of the dialogue. Jon Finch used to send notes to Alfred Hitchcock's secretary with suggested improvements. Hitchcock was not always pleased at this: "Jon, I said you could make alterations. I didn't say you could rewrite the whole script." However many of Finch's script amendments were indeed used in the final film.
- What Could Have Been:
- Around 1967, Hitchcock worked on a film concept about a handsome, charming young body-builder who happens to be a Serial Killer. It was to be set in New York City and told from the POV of the murderer, and to feature nudity and violence beyond anything ever shown on screen at that time. After the murderer kills twice the climax was to come when NYC police set up a trap with a policewoman posing as a potential victim. The project, which he alternately called Kaleidoscope and Frenzy, was rejected by Universal and then abandoned by Hitchcock. According to a biography on Hitchcock, the director himself shelved it because he couldn't think of a better ending. Hitchcock simply found the policewoman trap to be too cliché an ending after the excitement of the first two acts. Then in 1970 he read Arthur La Bern's Goodbye Piccadilly, Farewell Leicester Square and realized that he could rework some of the elements from the abandoned project into another serial killer tale. Also he decided to resurrect Frenzy as the title. Hitchcock fans and experts generally call the abandoned film Kaleidoscope to avoid confusion.
- Frenzy has the unenviable distinction of being the only time a Henry Mancini film score was thrown out; Mancini recorded the music in December 1971, but Hitchcock rejected it on the grounds that it was macabre, "which puzzled (Mancini) because it was a film with many macabre things in it." Ron Goodwin rescored the movie.
- Alfred Hitchcock wrote the role of Rusk with Michael Caine in mind originally (which becomes exceedingly obvious from his looks and clothing), but Caine turned it down because he was disgusted by the character and wished not to be associated with him. After Caine declined the role he later mentioned in his memoirs how Hitchcock completely ignored him when they met in a hotel a few years later.
- Helen Mirren was Hitchcock's first choice to play Babs Milligan and even met with the director before turning down the role, which years later she regretted.
- Vanessa Redgrave reportedly turned down the role of Brenda, and David Hemmings was considered to play Blaney.
- Laurence Olivier was considered for Chief Inspector Oxford. He'd played a similar character in Bunny Lake is Missing (both films also share Anna Massey in the cast).
Trivia / Frenzy