Arnold Schwarzenegger had a few conditions before accepting the role of John Kimble; he wanted Ivan Reitman to direct the film, he wanted a physical fitness theme, and he and Reitman wanted broken homes, child abuse and family life written into the script.
Owning a pet ferret, like Kimble does, is illegal in California - a ban which former governor Arnold Schwarzenegger supported, fortunately this film is set (and filmed partially) in Astoria Oregon where it is perfectly legal.
Arnold Schwarzenegger worked with Pamela Reed again in the movie Junior (1994) which was also directed by Ivan Reitman . Reed portrayed a pregnant woman with a big appetite, quite similar to her character in this movie. He also worked with Danny DeVito in Junior (1994), a candidate for the role of John Kimble, but was not given the part due to his height.
The trivia item below may give away important plot points.
Throughout the entire movie Kimball continues to assure people that the ferret doesn't bite. Ironically, at the climax of the movie, Domenic is saved when the ferret crawls out of his jacket and bites Crisp in the neck.