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

Donald Elson

Curator

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)

Sam Chew Jr.

Undetermined (uncredited)

Walker Edmiston

Talking Baby Chimp (uncredited) (voice)

Bob Harks

Aide (uncredited)

Linda Harrison

Nova (archive footage) (uncredited)

Elizabeth Harrower

Reporter at Hotel (uncredited)

Shep Houghton

Bystander (uncredited)

Robert Nichols

Reporter (uncredited)

Hank Robinson

Reporter (uncredited)

James B. Sikking

Control Room Officer (uncredited)

Arthur Tovey

Official at Briefing (uncredited)

William Tregoe

Hotel Receptionist (uncredited)

William Beckley

British News Anchor (uncredited)