Chuck Jones had been under an exclusive contract with Warner Bros. Pictures, and worked on this film as a screenwriter in violation of his contract. When WB picked up the film from UPA for distribution, they discovered his work on the film and immediately fired him on the spot, resulting in him to move to Metro-Goldwyn-Mayer.
When Judy Garland was approached about doing this film, it was she who reportedly suggested that her two good friends (and The Wizard of Oz (1939) collaborators) Harold Arlen and E.Y. Harburg provide the music and lyrics, respectively. It was to be both men's last full-length score for any medium.
Golden Books' children's division published a "Little Golden Books" version of "Gay Purr-ee" to coincide with the original theatrical release of the film.
The first animated feature film from Warner Bros. Pictures.