Rutger Hauer lost his mother and his best friend during the production of this movie. He returned to his native Netherlands for both of their respective funerals, but returned to the production each time within a few days. Despite all of the personal drama and all the difficulties on the set, Hauer stated in his autobiography that he was happy he stayed aboard as this movie caused him to be noticed in Hollywood and started an impressive international career.
Stories about on-set fights between Rutger Hauer and Sylvester Stallone are still talked about amongst fans of this movie and both actors. In his autobiography, Hauer stated that Stallone had come off a recent string of box office bombs, and was in desperate need of a hit movie. Hauer felt that many of the on-set clashes stemmed from Stallone's constant efforts to keep tight control over every aspect of the film's production (such as replacing original director Gary Nelson with Bruce Malmuth). However, Hauer also said during interviews in later years that he actually didn't take his arguments with Stallone personally, and that the biggest problem during filming was that it was a very difficult movie to make. From his part, Stallone has expressed deep regret over his behavior in the 1980s during a 2014 interview, stating that the success of Rocky (1976) had made him "insufferable"; by his own admission, he "abused power and was an authority on everything", and wished that he "could go back and punch myself in the face".
Sylvester Stallone said of the cable-car stunt to "Ain't It Cool News": "Hanging from the cable car was probably one of the more dangerous stunts I was asked to perform because it was untested and I was asked to hold a folding Gerber knife in my left hand so if the cable were to snap, and I survived the two hundred thirty foot fall into the East River with its ice cold eight mile an hour current, I could cut myself free from the harness because the cable when stretched out weighed more than three hundred pounds. I tell you this, because it's so stupid to believe that I would survive hitting the water. So to go beyond that is absurd."
The story was originally planned as The French Connection III by screenwriter David Shaber at Twentieth Century Fox, and would have seen Gene Hackman's Popeye Doyle team up with a wisecracking police officer, to be possibly played by Richard Pryor. The main plot was the same, but when Hackman showed reluctance to do a third movie as Doyle, the idea was scrapped and Universal Pictures acquired the rights to the storyline, which Saber then re-worked into this movie.
According to an interview in Premiere Magazine, Rutger Hauer was told before filming that Sylvester Stallone ran up building stairwells for exercise. However, during the subway chase, Hauer continually outran the American star, who is known for his competitive streak.