The play, on which the film is based, is done in three acts; act one is the final dress rehearsal; act two is the matinee performance; act three is the evening performance. The bridge scenes, with Sir Michael Caine's voiceover narration, including the opening scene, where he leaves the theater, and the ending scene where he returns, were written for the film, and do not appear in the play. In the play, the last line is the frantic call for "Curtain!"
The original Broadway production of "Noises Off!" by Michael Frayn, opened on December 11, 1983, at the Brooks Atkinson Theater, running for 553 performances, with a cast that included Victor Garber and Dorothy Loudon, and received a nomination for the 1984 Tony Award for Best Play.
Two of the characters names are changed from the original stage play: Lloyd Dallas (the director) and Frederick Fellows (the actor). In the movie version they are Lloyd Fellows (the director) and Frederick Dallas (the actor).
Lloyd's speech and rant to Tim, before the matinée, about the problems he's having directing Hamlet, was changed from the play. In the play, Lloyd is directing a production of Richard III, and all the characters and references reflect that. It was changed in the movie, because it was felt that Hamlet would be better-known to American audiences.
Although most of the dialogue was taken directly from the play, many words were changed to make the film more understandable for American audiences. Examples include "fortnight" being changed to "two weeks", "technical" being changed to "tech rehearsal", and "sixteen" being changed to "eighteen" (when referring to the age of consent).
The trivia item below may give away important plot points.
The film reveals that, in the Lloyd-Poppy-Brooke love triangle, Lloyd ends up choosing Poppy and the two get married. Although the play shares the plot point of Poppy's pregnancy, it is never revealed who Lloyd ends up with, or even if he stays with either woman.