Vic Perrin
Control Voice (voice) (uncredited)

Ivan Dixon
Sgt. James Conover / Major Harold Giles

John Hoyt
Professor Hebbel / Emmett Balfour / Bifrost Alien

Robert Culp
Trent / Paul Cameron / Allen Leighton

Robert Duvall
Adam Ballard / Louis Mace

Willard Sage
Coulter / First Reporter / Chief of Staff

Jason Wingreen
Fred Severn / Coroner Leland / Bill Turner

Edward Platt
Mr. Terrence / David Hunt (as Edward C. Platt) / Dean Radcliffe

Douglas Henderson
Dr. Paul Fredericks (uncredited) / Dr. Tillyard / Detective Lt. Runyan

Ben Wright
Elder of Luminos / Philip Exeter Dundee / Gen. Benton

Robert Fortier
Bert Hamil / Budge / Dr. Paul Pollard

Ted de Corsia
Randolph E. Branch / New Sentry

Dabney Coleman
Dr. Williams / Lt. Rupert Lawrence Howard (uncredited) / James Custer

David Frankham
Harvey Kry Jr. / Capt. Terrence Ralph Brookman

Philip Abbott
Lincoln Russell / Ben Fields

Henry Silva
General Juan Mercurio / Chino Rivera

Kent Smith
Aabel / Dr. Block

Janos Prohaska
Thetan (uncredited) / The Mikie

William Stevens
Navigator Dexter / Policeman

Geraldine Brooks
Yvette Leighton / Ann Barton