For its French release, Marlene Jobert (Fabienne) was billed above Kirk Douglas (Andrej).
Dick Clement later said Kirk Douglas requested a meeting before filming started. "Being an American, Douglas got straight to the point. He said I can't play comedy. And do you know what - he couldn't."
Tom Courtenay (who was not yet Sir Tom Courtenay) had returned to film after a two year absence: In 1969 he starred in the same director's other spy comedy, Otley, and this would be the last theatrical motion picture Courtenay appeared in until The Dresser in 1983. He worked mainly on stage, and a few television movies.
Kirk Douglas is most oddly cast as a Bulgarian. However, he doesn't attempt the accent, and speaks in his normal American voice. This is not explained.
Photoplay Magazine reported that Kirk Douglas was planning to buy a U.K. residence after his happy experience filming this movie.