When Jack Nicholson would get ready to play his nude scenes, he'd prepare everyone on set by warning, "Here comes Big Steve!"
The fight scene between Nicholson and Ann-Margret took a week to shoot, and at the end of it both performers had lost their voices.
After auditioning several actresses for the role of Bobbi, Mike Nichols agreed to see Ann-Margret, whom he remembered being very impressed with in Kitten with a Whip (1964).
The scene in which Sandy takes out a condom while in bed with Susan is the first time a condom was ever shown onscreen.
After working with Jack Nicholson in Easy Rider (1969), Karen Black went to Mike Nichols, on recommendation from Jack, to test for the role of Bobbie. It was mutually decided that Karen did not have the right figure for the role.
Writer Jules Feiffer originally pitched the concept to director Mike Nichols as a theatre project. After listening to Feiffer's ideas, Nichols said, "I see it as a movie."
Ellen Burstyn auditioned for the role of Bobbi. After seeing the finished film, however, Burstyn admitted she could not have played the role as well as Ann-Margret did.