Becky and Miles paraphrase Shakespeare twice. "I know a bank whereon the wild thyme blows, Where oxlips and the nodding violet grows" is from A Midsummer Night's Dream. "That way madness lies" is from King Lear.
Only $15,000 of the budget was spent on special effects.
Ranked #9 on the American Film Institute's list of the 10 greatest films in the genre "Sci-Fi" in June 2008.
The film originally ended with Miles J. Binnell on the highway shouting to the people driving by, "You're next, you're next!" However, the studio wanted a happier ending that would assure the audience that the hero's efforts were not in vain, so scenes were added to the opening to show Miles in a hospital recounting his story to two other doctors and to the end when the other doctors find out about the pods and one of them contacts the FBI.
The tunnel scene where the hero hides briefly from the townspeople was filmed at Bronson Cave in Griffith Park, famous with locals as the Bat Cave.
Throughout the years, Sam Peckinpah (who appears briefly in the film as the meter reader) claimed that he had done work on the script ranging from modifications to major overhauls. Those who worked on the film claimed that if Peckinpah had made any changes to the script, it was limited to a few lines of dialog. Peckinpah's claims became so inflated that the actual writer, Daniel Mainwaring, threatened to file an official complaint with the Writers Guild of America, so Peckinpah backed down. When Peckinpah died in 1984, many of his obituaries still carried the claim that he had rewritten the screenplay for this film.
Universal's UK DVD (824 346 1.11) comes with a choice of the original black and white or a colorized version. The black & white's running time is 1hr and 20 mins while the color version has an added five minutes to its running time.