This pilot film for the popular medical drama turned out to be the only shared credit of Edward G. Robinson, who was originally cast to play Dr. Zaius in the preceding year's Planet of the Apes (1968), and Maurice Evans who ended up playing the role in the finished film and its first sequel Beneath the Planet of the Apes (1970). Test footage had even been shot with Robinson in an early version of the simian makeup, acting opposite Charlton Heston who would be the film's star and also appear in that next installment, Linda Harrison who would play Nova in those same two first films of the saga (in the test footage as the originally intended Zira) and James Brolin (as the originally intended Cornelius) who would not finally appear in any of the "Apes" films although he would go on to play Dr. Steven Kiley in this series' main rival medical drama Marcus Welby, M.D. (1969). Also present in this pilot, the original "Apes" film would also star James Daly who would continue his role here as Dr. Paul Lochner throughout the "Medical Center" series. And another actor here, William Windom, would appear in the third "Apes" film Escape from the Planet of the Apes (1971) playing the President of the United States.
CBS test audiences for this pilot did not like Richard Bradford in the lead role, so he was replaced by Chad Everett.
Co-starring in a minor role in this pilot is Tim O'Kelly, who suffered the same fate as Richard Bradford did, but on another CBS pilot that aired at about the same time this pilot was originally aired. O'Kelly was originally cast as Danny Williams in the pilot for Hawaii Five-O (1968), but did not test well with audiences, so he was replaced with James MacArthur.