Vic Perrin
Control Voice (voice) (uncredited)

Ivan Dixon
Sgt. James Conover / Major Harold Giles

John Hoyt
Emmett Balfour / Professor Hebbel / Bifrost Alien

Robert Culp
Allen Leighton / Paul Cameron / Trent

Robert Duvall
Adam Ballard / Louis Mace

Willard Sage
Chief of Staff / First Reporter / Coulter

Jason Wingreen
Coroner Leland / Bill Turner / Fred Severn

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

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

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 / James Custer / Lt. Rupert Lawrence Howard (uncredited)

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

Philip Abbott
Ben Fields / Lincoln Russell

Henry Silva
General Juan Mercurio / Chino Rivera

Kent Smith
Aabel / Dr. Block

William Stevens
Policeman / Navigator Dexter

Janos Prohaska
The Mikie / Thetan (uncredited)

Martin Landau
Andro / Richard Bellero