Lee Grant claimed in her 2014 autobiography that "everyone knew" Goldie Hawn and Warren Beatty were sleeping together, even though he was still involved with Julie Christie.
Lovers off and on since 1967, Warren Beatty and Julie Christie broke up for good during the making of this movie. They remained friends and later worked together in Heaven Can Wait (1978).
Carrie Fisher said she was cast in the role mainly through family connections. She said when Warren Beatty ran lines with her, he did it whilst eating. She said the whole thing for her was a lark. She also admitted years later in an article she wrote for Rolling Stone magazine that star Beatty unsuccessfully propositioned her.
When Warren Beatty conceived the idea for this film in 1967, it was called 'Hair' (later changed to avoid confusion with the rock musical).