After years of alcoholism and prescription drug abuse, Montgomery Clift was considered uninsurable due to chronic ill health. Ordinarily, he would have been fired and replaced, but his good friend Dame Elizabeth Taylor saved his job by insisting she would not do this movie without him.
According to author Garson Kanin in his memoir "Tracy and Hepburn," Katharine Hepburn was reportedly so furious at the way Montgomery Clift was treated by producer Sam Spiegel and director Joseph L. Mankiewicz during filming that, after making sure that she would not be needed for retakes, she told both men off and actually spat at them (although it remains unclear just which one of the two she spat at, or if she spat at both).
Peter O'Toole did a disastrous screen test. In fact, it went so badly that when he was being considered for the lead in Lawrence d'Arabie (1962), producer Sam Spiegel -who produced both movies -didn't want anything to do with O'Toole again.
In performing Catherine Holly's climactic monologue, Dame Elizabeth Taylor (who had recently been widowed) reportedly used her emotions about her husband's death in order to create the acclaimed performance. However, she was only able to do one take, as she could not stop crying after completing the first.
According to Mercedes McCambridge, she rode to the London set of this movie in the same car as Montgomery Clift. He always insisted that the driver stop by Wormwood Scrubs prison, so that he could scream out the car window at the convicts behind bars.