Roddy McDowall
Cornelius
Kim Hunter
Dr. Zira
Bradford Dillman
Dr. Lewis Dixon
Natalie Trundy
Dr. Stephanie 'Stevie' Branton
Eric Braeden
Dr. Otto Hasslein
William Windom
The President
Sal Mineo
Dr. Milo
Albert Salmi
E-1
Jason Evers
E-2
John Randolph
Committee Chairman
Harry Lauter
General Winthrop
M. Emmet Walsh
Aide
Roy Glenn
Lawyer (as Roy E. Glenn Sr.)
Peter Forster
Cardinal
Norman Burton
Army Officer
William Woodson
Naval Officer
Tom Lowell
Orderly
Gene Whittington
Marine Captain
Donald Elson
Curator
Bill Bonds
TV Newscaster
Army Archerd
Referee
James Bacon
General Faulkner
Ricardo Montalban
Armando
John Alderman
Marine Corporal (uncredited)
Alan Baxter
General (uncredited)
Jack Berle
Secretary of State (uncredited)
Paul Bradley
Official at Briefing (uncredited)
Karl Bruck
German Newscaster (uncredited)
Sam Chew Jr.
Undetermined (uncredited)
Robert Cole
Reporter (uncredited)
Walker Edmiston
Talking Baby Chimp (uncredited) (voice)
Sig Frohlich
Spectator (uncredited)
James W. Gavin
Helicopter Pilot (uncredited)
George Golden
Official at Briefing (uncredited)
James Gonzalez
Official at Briefing (uncredited)
Joe Gray
Bodyguard (uncredited)
Bob Harks
Aide (uncredited)
Linda Harrison
Nova (archive footage) (uncredited)
Elizabeth Harrower
Reporter at Hotel (uncredited)
Shep Houghton
Bystander (uncredited)
Joseph La Cava
Waiter (uncredited)
Robert Nichols
Reporter (uncredited)
Ron Pinkard
Undetermined (uncredited)
Janos Prohaska
Heloise (uncredited)
Tony Regan
Reporter at Hotel (uncredited)
Stephen Roberts
Gen. Brody (uncredited)
Hank Robinson
Reporter (uncredited)
James B. Sikking
Control Room Officer (uncredited)
Jack Slate
Reporter (uncredited)
Arthur Tovey
Official at Briefing (uncredited)
William Tregoe
Hotel Receptionist (uncredited)
William Beckley
British News Anchor (uncredited)