Sutherland and Fonda developed a nonexclusive romantic relationship offscreen which lasted until about June 1972. He was her date to the Oscars when she won Best Actress for this movie.
Future film star Sylvester Stallone made an appearance as an extra in this film. He's the one dancing in front of the organ pipes during the first disco scene.
Klute was only the second film score for Michael Small, who said that Pakula took a big risk here to work with an unknown composer.
Bree's apartment was built on a sound stage at a New York film studio where Jane Fonda could spend the night. The director even had a working toilet installed in the bathroom of the set. Jane contributed to decorating the apartment by deciding Bree would be a romance reader and have a cat. Jane remembered an actress from Lee Strasberg's private class who occasionally serviced John F. Kennedy, so she decided Bree had done this as well. A signed photo of Kennedy appears on wall above the dressing table in Bree's apartment.
The first installment of what informally came to be known as Pakula's "paranoia trilogy." The other two films in the trilogy are À cause d'un assassinat (1974) and All the President's Men (1976).