The use of a split-focus diopter lens is evident in several scenes, in particular the sound recording scene and the hospital scene. The split-focus lens is attached to the main lens, and it affects only the left or right portion of the main lens' view. This changes the focal distance of part of the image, allowing objects at two distances (in the foreground and background) to be in sharp focus.
During the editing process, two reels of footage from the Liberty Parade sequence were stolen and were never to be seen again. This meant that the scenes had to be reshot at a cost of $750,000. Cinematographer Vilmos Zsigmond was no longer available, so he was replaced by László Kovács.
Al Pacino was director Brian De Palma's first choice for the role of Jack Terry. When he proved unavailable John Travolta was signed, prompting a suggestion from at least one studio executive to cast Olivia Newton-John, Travolta's Grease (1978) co-star, in the role of Sally (which De Palma refused).
The underwater components of the car crash on the bridge set piece were shot in a huge tank in California. Nancy Allen suffers from claustrophobia and hence had a hard time with being trapped in the car in the underwater scenes.