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.
The original copyright was apparently never renewed, and the film fell into public domain, with the result that a multitude of low cost, low quality, VHS and dupes flooded the videotape market, and were broadcast by independent cable and television stations who did not have access to the original material.
Four different endings were filmed, but all were ultimately deemed unsatisfactory during previews. A letter from an audience member suggested a fifth ending, which Frank Capra liked and used in the finished 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.
Frank Capra went into production without a clear idea of how the film should end. He shot or edited five endings and previewed two. In one, the film ended with John being disgraced at the John Doe Convention and Henry Connell saying, "Well, boys, you can chalk another one up to the Pontius Pilates." Preview audiences found that version too depressing. Another ending actually had John committing suicide, with The Colonel cradling his dead body in his arms and saying "Long John, you poor fool. You poor sucker." Robert Riskin preferred this ending, but Capra was unconvinced, and feared the suicide would cause problems with the Catholic Church. He also had a version in which Ann talks John out of committing suicide and a variation in which John's merry Christmas with Henry causes the corrupt publisher to see the light. Undecided, Capra released different versions of the ending for the film's initial engagements in Los Angeles, San Francisco and Washington, DC. Finally, a comment from one of the previews inspired a fifth ending, in which some of the original John Doe Club members show up to tell Willoughby they had never stopped believing in him. That also would allow Capra to deal with another problem pointed out by preview audiences and in letters from angry fans - the depiction of Cooper's followers as a fickle herd easily swayed by the film's corrupt politicians. Capra shot the new ending and had prints called back from theatres so it could be added before the film went into national release. Years later he would say that even that ending wasn't quite right.
Although the film seemed poised to make a handsome profit for Frank Capra and Robert Riskin, under current federal laws they were required to pay taxes on the income before the profits even came in. Without studio overhead and a steady stream of pictures to keep money rolling in, they had to dissolve their corporation simply to pay taxes on the film. Capra would have to postpone his dream of producing his own films for years because of that.
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 (1940): 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'.
Regis Toomey had already memorized his monologue about the John Doe Clubs for his audition, so the day he was supposed to shoot it, Frank Capra asked if he needed a rehearsal. Toomey didn't, so they shot the scene in one take.
Well into production, Frank Capra refused to reveal publicly what the film was about. Part of the motivation for his secrecy was fear that U.S. Fascist groups would pressure Warner Bros. not to make the film. But he also did not have a completed screenplay, and keeping mum on the film's subject was his way of keeping Warner Bros. from pulling out of their agreement.
The rooftop set for the final scene in was built in an icehouse to capture the sense that it was taking place on Christmas Eve. Barbara Stanwyck later said after shooting the scene she had to go to "the hospital for a defrost."