According to Kramer, he and Rose intentionally structured the film to debunk ethnic stereotypes. The young doctor, a typical role for the young Sidney Poitier, was created idealistically perfect, so that the only possible objections to his marrying Joanna would be his race, or the fact she had only known him for 10 days; the character has thus graduated from a top school, begun innovative medical initiatives in Africa, refused to have premarital sex with his fiancée despite her willingness, and leaves money in an open container on his future father-in-law's desk in payment for a long-distance phone call he has made. Kramer and Rose completed the film script in five weeks.[10]
Kramer stated later that the principal actors believed so strongly in the premise that they agreed to act in the project even before seeing the script. Production had been set for January 1967 and ended on May 24, 1967.[11] At age 67, Tracy was in poor health with heart disease, diabetes, high-blood pressure, respiratory disease, and other ailments. Aware of Tracy's declining health, insurance companies refused to cover him for the period of filming. Kramer and Hepburn put their salaries in escrow so that if he should die during the production, filming could be completed with another actor. According to Kramer, "You're never examined for insurance until a few weeks before a picture starts. [Even] with all his drinking and ailments, Tracy always qualified for insurance before, so nobody thought it would be a problem in this case. But it was. We couldn't get insurance for Spence. The situation looked desperate. So then we figured out a way of handling it. Kate and I put up our own salaries to compensate for the lack of an insurance company for Spence. And we were allowed to proceed."[12]
The filming schedule was altered to accommodate Tracy's failing health.[13] All of Tracy's scenes and shots were filmed between 9:00 am and noon of each day to give him adequate time to rest for the remainder of the day.[10] For example, most of Tracy's dialogue scenes were filmed in such a way that during close-ups on other characters, a stand-in was substituted for him.[14]
Tracy's failing health was more serious than most people working on the set were aware of. According to Poitier: "The illness of Spencer dominated everything. I knew his health was very poor and many of the people who knew what the situation was didn't believe we'd finish the film, that is, that Tracy would be able to finish the film. Those of us who were close knew it was worse than they thought. Kate brought him to and from the set. She worked with him on his lines. She made sure with [Stanley] Kramer that his hours were right for what he could do, and what he couldn't do was different each day. There were days when he couldn't do anything. But also there were days when he was great, and I got the chance to know what it was like working with Tracy."[15]
A bust of Tracy sculpted by Hepburn herself was used as a prop, on the bookshelf behind the desk where Poitier makes his phone call.
Tracy died two weeks after he completed his work on the film.[16]
Hepburn significantly helped cast her niece, Katharine Houghton, for the role of Joey Drayton. Concerning this, Hepburn stated: "There was a lovely part for Kathy [Houghton], my niece [...] She would play Spencer's and my daughter. I loved that. She's beautiful and she definitely had a family resemblance. It was my idea."[17]
According to Hepburn, the role of Joey Drayton was one of Houghton's first major roles as a young actress. "The part of my daughter," Kate said, "was a difficult one. A young unknown actress needs more opportunity to win the sympathy of the audience. Otherwise, too much has to depend on her youth, innocence, and beauty. She had one good speech to win the audience, but it was cut. Instead she only talks with her father about the differences between the principles he taught her and the way he's behaving."[18]
Poitier frequently found himself starstruck, and as a result, a bit tongue-tied in the presence of Hepburn and Tracy, whom he considered to be "giants" as far as acting is concerned.[19] However, Poitier reportedly found a way to overcome his nerves. "When I went to play a scene with Tracy and Hepburn, I couldn't remember a word. Finally, Stanley Kramer said to me, 'What are we going to do?' I said, 'Stanley, send those two people home. I will play the scene against two empty chairs. I don't want them here because I can't handle that kind of company.' He sent them home. I played the scene in close-up against two empty chairs as the dialogue coach read Mr. Tracy's and Miss Hepburn's lines from off camera."[19]
Given the tense nature of racism in the United States during the time of the film's production, Poitier felt he was "under close observation" by both Tracy and Hepburn during their first dinner meetings prior to production.[20] However, he managed to swiftly win them over. Due to Tracy and Hepburn's close history with Kramer, Poitier cited that Hepburn and Tracy came to bear on him "the kind of respect they had for Kramer, and they had to say to themselves (and I'm sure they did), this kid has to be pretty okay, because Stanley is nuts about working with him".[21]
