Joseph Barbera, of Hanna-Barbera cartoons fame, had an idea to make a movie about ambulance driving. Twentieth Century Fox gave him development money to deliver a script. Barbera heard that screenwriter Tom Mankiewicz, who'd written several James Bond movies, was interested, and hired him. Barbera set up Mankiewicz with a local ambulance company for some "real world" experience. Mankiewicz rode in an ambulance driven by Tom "Hap" Hazard, and witnessed the results of a stabbing on the Sunset Strip, as well as potential suicide and heart attack victims. After these ride-alongs, Mankiewicz know he had the makings of a terrific movie, and wrote the original script for this movie.
Producer and screenwriter Tom Mankiewicz was at a party at Natalie Wood's house when he met Peter Yates, who had directed Bullitt (1968) with Steve McQueen. When asked what his next project might be, Yates said he'd love to do a comedy with some "bite" to it. Mankiewicz got a copy of this movie's script out of the trunk of his car, and Yates agreed to read it on his transatlantic flight home to England. Yates called Mankiewicz the next morning and said, "Let's do it."
The new head of production at Twentieth Century Fox, Alan Ladd, Jr., after reading a copy of the script, said, "This is about the most offensive script I've ever read in my life. There is no group you don't insult in this move. Can you make this for three million bucks?"
Larry Hagman was described by Tom Mankiewicz as "totally nuts", arriving on the set one day dressed as an astronaut, and the next day as a World War I French General.
The tight budget imposed by Twentieth Century Fox meant the leads had to accept deferred payments for making this movie. Bill Cosby (Mother) and Harvey Keitel (Speed) agreed to the deferred money. The producers wanted Valerie Perrine to play "Jugs", but she wouldn't defer any money. Raquel Welch wanted the part badly, and would work for deferred money, so she was cast instead.