Robert Wagner wrote in his autobiography that Raquel Welch was constantly late on the set, keeping the cast and crew waiting for hours while she had her hair and make-up done. Finally, Edward G. Robinson cracked, telling Welch off in an angry ten minute tirade which left Welch in tears and apologizing for her behavior. However, Wagner writes, the next day, she was late again. Director Ken Annakin also recalled, in a later interview, that not only was she constantly late, but that she "tended to wing her lines a little bit." He then told her if she didn't show up on time knowing her lines he would use as little of her as possible and not use her in any close-ups - just medium and long shots. "She was very co-operative after that", Annakin said.
Although filming wrapped in August of 1966, this film's release was delayed until early 1968 because Columbia discovered this picture had a similar plot to Les détraqués (1967). Sam Spiegel, a producer on that film agreed not to sue MGM in exchange for a percentage of the profits from this film, rumored to be close to 25%, and a delayed release of eight months after Columbia's picture opened.
Professor Samuels (Edward G. Robinson) produces an ounce of platinum and says it's worth $95 an ounce. In 2021, that amount is equivalent to around $760.
In the physical training scene, Robert Wagner is wearing a sweatshirt that says "Black Fox Prep School" on the front. This is a nod to the Black-Foxe Military Institute in Hollywood he attended in the 1940s. Godfrey Cambridge, a native of New York City, is wearing a New York Academy of Music t-shirt.
Celli is kidnapped at the beginning of the film in a 1956 Imperial Crown limousine. One of only 175 made, an example sold at auction in 2015 for nearly $150,000.