In the scene near the end where Spencer Tracy gives his memorable soliloquy, Katharine Hepburn can be seen crying in the background. This was not acting: she knew how gravely ill her longtime friend and lover was and was moved by his remarks about how true love endures through the years.
Katharine Hepburn had to use her salary as backing in order to make this movie because Spencer Tracy was so ill that the studio didn't think that he would make it to the end of the picture. They didn't want to insure an actor who could possibly die in the middle of production but she refused to do the movie without him. He died 17 days after he finished filming his scenes.
The film's last scene was Spencer Tracy's last scene ever filmed. It took a week to shoot the scene, and at the end, he was given a standing ovation by the crew. He died seventeen days after filming was completed.
This movie was still showing in theaters at the time Dr. Martin Luther King, Jr., was assassinated. There is a line in the movie where Joey (Katharine Houghton) tells the maid another person is coming to dinner, to which Tillie (Isabel Sanford), the maid guesses, "The Reverend Martin Luther King?" When King was murdered, the studio immediately called the theaters showing the film and gave instructions to cut the scene.