"The Screen Guild Theater" broadcast a 30 minute radio adaptation of the movie on September 28, 1941 with Gary Cooper, Barbara Stanwyck and Edward Arnold reprising their film roles.
Frank Capra didn't want anyone to play John Doe except Gary Cooper, who agreed to the part (without reading a script) for two reasons: he had enjoyed working with Capra on Mr. Deeds Goes to Town and he wanted to work with Barbara Stanwyck.
Frank Capra's first choice for the role of Ann Mitchell was Ann Sheridan. However, she was vetoed by Warner Bros. in a contract dispute.
Contrary to popular belief, there is no "longer" version of this film. The film has always run 123 minutes. However, the original publicity erroneously stated it was 132 minutes; the publicist accidentally flipped the last two numbers. For years, historians assumed that all reissue prints had been cut by 9 minutes, until an original fine grain master was uncovered, and also turned out to run 123 minutes. This is the only running time for the film.
Director Frank Capra tested the film in different areas of the US with four different endings to determine which one to keep. In one, John Willoughby commits suicide. In another, Ann Mitchell persuades him not to leap from City Hall. Inspired by a letter signed "John Doe," Capra filmed a fifth and final ending in which Mitchell talks some sense into Willoughby and then faints into his arms.
Regarding the 'sweet potatoes' that Gary Cooper and Walter Brennan play, in addition to "Hi Diddle Dee Dee (An Actor's Life For Me)", from "Pinocchio": Brennan alone plays this on an ocarina (sweet potato), but Cooper plays a small harmonica. The tune they play as a duet, while Barbara Stanwyck is interviewing them, is The "William Tell Overture, Finale" by Rossini (The Lone Ranger Theme). Cooper explains the reason Brennan likes him is that they both play 'Doohickeys'.
The first film Frank Capra produced independent of the Hollywood studios.
The tune that the main characters constantly play on their sweet potatoes is "Hi-Diddle-Dee-Dee (An Actor's Life for Me)" from Pinocchio