Director Stanley Kramer hired real biker gangs to play themselves. When Kramer asked one of them what they were rebelling against, one cyclist cracked, "Well, what ya got?" That was incorporated into the script and became one of the film's most quoted lines.
Lee Marvin was actually drunk in several of his scenes, and his on-screen rivalry with Marlon Brando continued off-camera as well.
This film was banned in the U.K. for 15 years, until 1968.