Stanley Kubrick was originally interested in adapting Lionel White's "The Snatchers", upon which this movie was based. However, due to a ban on the subject of kidnapping in the 1950s, Kubrick opted to do The Killing, which was also based upon a Lionel White story.
Hubert Cornfield, on the Universal DVD commentary, claims that Marlon Brando in an attempt to humiliate him, tried to seduce Cornfield's wife and, after being turned down, went to tell Cornfield about his efforts. Cornfield told him that he was flattered.
At Marlon Brando's insistence, the last scenes of the shooting schedule were directed by Richard Boone, as Brando could no longer stand for what he considered the incompetence of director Hubert Cornfield.
In the scene in which Rita Moreno is in the tub zonked out on heroin, Marlon Brando entered the set completely drunk and played the scene in that condition. In the editing room director Hubert Cornfield had to delete the parts in which his drunkenness was apparent.
The final shot, with Marlon Brando smiling in a close-up, was particularly difficult to film for director Hubert Cornfield. Brando kept on making silly faces and refused to smile because he was upset that the ending he preferred was not filmed. In the editing room, Cornfield picked out one frame in which Brando smiled before making another face.
The original intention was to have Richard Boone play Marlon Brando's role. However, co-producer Elliott Kastner came back to director/co-writer Hubert Cornfield and told him there was a possibility they could get Marlon Brando for the part. Cornfield jumped at the chance.