Eric Braeden as Dr Charles Forbin

Susan Clark as Dr. Cleo Markham

Gordon Pinsent as The President

William Schallert as CIA Director Grauber

Georg Stanford Brown as Dr. John F. Fisher

Willard Sage as Dr. Blake

Alex Rodine as Dr. Kuprin

Martin E. Brooks as Dr. Jefferson J. Johnson

Marion Ross as Angela Fields

Dolph Sweet as Missile Commander

Byron Morrow as Secretary of State

Lew Brown as Peterson

Sid McCoy as Secretary of Defense

James Hong as Dr. Chin

Robert Cornthwaite as First Scientist

Tom Basham as Thomas L. Harrison

Leonid Rostoff as Russian Chairman

Serge Tschernisch as Translator

John Davey as Military officer on phone (uncredited)

Paul Frees as Colossus (voice) (uncredited)

Fred Holliday as Military Computer Entry - Missile Launch (uncredited)

Robert Quarry as Scientist (uncredited)

Don Ross as Logan US Air Force (uncredited)

William Traylor as Party Guest (uncredited)