Albert Brooks was under a great deal of pressure to finish the film on-budget, because he would have been personally responsible for any extra costs. During one particularly difficult filming day, he sat feeling totally dejected. Charles Grodin walked up to him and said, "I have to leave at 4." This totally ridiculous request was sufficient to cheer Brooks up.
Charles H. Reid, who plays the assistant surgeon, was a real veterinarian who provided the horse that appears in the film.
One of the reasons Albert Brooks wanted to cast Charles Grodin as the father was because of Grodin's work on Candid Camera (1972). Brooks felt that Grodin would look like he wasn't acting, because on the TV show he had to fool ordinary people into believing that he wasn't acting.
The role-reversal family is played by the real family of Clifford Einstein, the older brother of Albert Brooks.
The final scene took three days to film due to constant noise from planes flying overhead. The soundstage was near the Van Nuys Airport.