During pre-production, one of the producers was set to meet with Quincy Jones, but he didn't know Jones was black. The producer saw Jones for the first time and told him, "I'll be right back", and the producer left with the intention of bringing in a non-black composer for the film. Shortly afterwards, Henry Mancini, a longtime personal friend of Jones, recommended him to the producer, thereby ensuring Jones getting hired to score the film.
Leslie Caron wrote in her book "Thank Heaven" that Universal offered her the film with Gregory Peck. But her then boyfriend, Warren Beatty, who was controlling her life, made her refuse it. Later she regretted declining the part, as she would have loved to make a film with Mr. Peck, with whom she became friends later on.
The television set at David's (Gregory Peck's) apartment was the Zenith with mechanical wireless remote control. The spring-loaded remote produces commands via the ultrasonic clicks which are picked up and processed by the television. You can clearly hear the specific loud click when David turns it off with the remote.
The line spoken by Lester (Jack Weston), "you can't be alive in Barbados and dead in New York at the same time", is paraphrased from a line in the Pat Novak For Hire radio program titled "Rubin Callaway's Pictures", with Detroit in Pat Novak changed to Barbados in this movie.