This was legendary Costume Designer Edith Head's final film. There is a tribute to her in the closing credits denoting this. Fittingly, the film features many of her earlier designs in cleverly edited clips from old movies.
Also the last film of legendary composer Miklós Rózsa. This was ironic since he was also asked to rescore music for original images that he had worked on in the 1940s and '50s.
The car accident at the beginning of the movie (the killing of the scientist) is taken from Keeper of the Flame (1942). That movie, however, is not listed in the credits as the source of the footage.
The movie was initially planned by Steve Martin and Carl Reiner to be a '30s-era film titled "Depression". After Reiner incorporated some footage of a '30s star into the movie, he and Martin decided that the entire movie should be done that way, and re-wrote it into a mock-detective story.
Rigby Reardon tells Lana Turner he left her sitting at a counter at Schwabs. Turner is rumored to have been discovered sitting at the counter in a Schwabs drugstore.
Initially, Steve Martin's character was written to tell off Humphrey Bogart's "mentor" character as an old has-been. The scene in which Martin did this was restored for network-TV showings.
While Steve Martin's character is at the bar in Carlotta, a clip is used of Charles Laughton from The Bribe (1949) asking, "You know who I could be?" and Martin replies, "The Hunchback of Notre Dame?" Laughton played that role in The Hunchback of Notre Dame (1939).
When Rigby Reardon (the character played by Steve Martin) finds the "Top Secret" Nazi packet labeled "Final Instructions", the date on the packet is 14 August 1946. Steve Martin's actual birth date is 14 August 1945.