- Roddy McDowall
- Cornelius
- Kim Hunter
- Dr. Zira
- Bradford Dillman
- Dr. Lewis Dixon
- Natalie Trundy
- Dr. Stephanie Branton/Stevie
- Eric Braeden
- Dr. Otto Hasslein
- William Windom
- The President
- Sal Mineo
- Dr. Milo
- Albert Salmi
- E-1
- Jason Evers
- E-2
- John Randolph
- Chairman of the President's Committee of Inquiry
- Harry Lauter
- General Winthrop
- M. Emmet Walsh
- General Winthrop's Aide
- Roy Glenn
- Lawyer
- Peter Forster
- Cardinal
- Norman Burton
- Army Officer
- Bill Woodson
- Naval Officer
- Tom Lowell
- Orderly
- Gene Whittington
- Marine Captain
- Donald Elson
- Curator
- Army Archerd
- Referee
- Bill Bonds
- TV Newscaster
- James Bacon
- General Faulkner
- Ricardo Montalban
- Armando
- John Alderman
- Marine Corporal (uncredited)
- Stephen Roberts
- General Brody (uncredited)
- Don Taylor
- Director
- Paul Dehn
- Writer
- Frank Capra Jr.
- Associate Producer
- Arthur P. Jacobs
- Producer
- Jerry Goldsmith
- Original Music
- Joseph F. Biroc
- Cinematographer
- Marion Rothman
- Film Editing
- William J. Creber
- Art Director
- Jack Martin Smith
- Art Director
- Stuart A. Reiss
- Set Decoration
- Walter M. Scott
- Set Decoration
- Mary Babcock
- Hair Stylist
- Jack Barron
- Makeup Artist
- Daniel C. Striepeke
- Makeup Supervisor
- Francisco Day
- Unit Production Manager
- Joseph Lenzi
- Assistant Director
- Theodore Soderberg
- Sound
- Dean Vernon
- Sound
