Lee Marvin drank real alcohol throughout the production, even though director Joshua Logan fought him about it. In most movies, the actors and actresses drink tea for whiskey and water for vodka. Marvin would only work if he got real liquor.
Jean Seberg's singing voice was dubbed by Anita Gordon. Clint Eastwood and Lee Marvin did their own singing. Marvin's recording of the song "Wanderin' Star" went to number one on the U.K. charts, earning him a gold record.
Jean Seberg (Elizabeth) described Lee Marvin's (Ben Rumson's) singing as "like rain gurgling down a rusty pipe".
Lee Marvin (Ben Rumson) was set to star in The Wild Bunch (1969), a project that he helped put together with stuntman Roy N. Sickner, when Paramount Pictures offered him $1 million, plus a percentage of the box-office take, to star in this movie.
Alan Jay Lerner: Singing while standing on the log next to William O'Connell during "There's a Coach Coming In."