Sean Connery turned down the role of Chris Flanders.
Topol passed on this project
James Fox was originally supposed to play Chris Flanders, but Elizabeth Taylor insisted that her husband Richard Burton should be cast instead. This was despite the fact that at 42 Burton was much older than the twenty-something character.
Tennessee Williams stated that it was the best film version of any of his plays that was ever produced. The rest of the world seemed not to agree, for the monumentally expensive production bombed at the box office.
James Bernard was considered to write the film score.
According to Lord Melvyn Bragg in his biography Richard Burton: A Life" (1988), director Joseph Losey was drinking heavily during the shooting of "Boom!" due to personal problems. Bragg attributes some of the responsibility for the failure of the film to this.
According to the book, "Infinite Variety" by Scot D. Ryersson and Michael Orlando Yaccarino, the characters of Flora Goforth and the Witch of Capri were both partly inspired by the infamous Italian eccentric and patron of the arts, the Marchesa Luisa Casati (1881-1957).
Chris as envisioned was a young poet, and Richard Burton was considered by most to be terribly miscast as well as too old for the part. The bust of "Boom!" seriously damaged Elizabeth Taylor's standing at the box office, though Burton had another major hit with Where Eagles Dare after the fiasco of its drubbing by both the critics and movie audiences.
Despite the twin Broadway failures of the play "The Milk Train Doesn't Stop Here Anymore," it was thought that Elizabeth Taylor and Tennessee Williams were an irresistible combination, after the sucess of Cat on a Hot Tin Roof and Suddenly, Last Summer, both of which won Taylor Oscar nominations as Best Actress. It was a fatal miscalculation on the part of the producer.
Tennesse Williams lobbied Sean Connery to play Chris, but he declined.
The first mainstream British film to include the expletive "shit" in its dialog (see Quotes section).
The movie is based on the Tennessee Williams' play "The Milk Train Doesn't Stop Here Anymore", which flopped on Broadway, closing on 16 March 1963 after just 69 performances. Director Tony Richardson, hot after the release of his film Tom Jones, directed the revival that opened with Tallulah Bankhead as Gloria Goforth and 'Tab Hunter' as Chris in January 1964. The revival was a disaster, closing after just 5 performances. The dual failures of "Milk Train" signalled the end of Williams' greatness as a playwright.
The play "The Milk Train Doesn't Stop Here Anymore", and thus this movie, are based on Tennessee Williams' short story "Man Bring This Up Road".