Vic Perrin
Control Voice (voice) (uncredited)

Ivan Dixon
Sgt. James Conover / Major Harold Giles

John Hoyt
Bifrost Alien / Professor Hebbel / Emmett Balfour

Robert Culp
Paul Cameron / Trent / Allen Leighton

Robert Duvall
Adam Ballard / Louis Mace

Willard Sage
Coulter / First Reporter / Chief of Staff

Jason Wingreen
Coroner Leland / Fred Severn / Bill Turner

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

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

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

Robert Fortier
Budge / Bert Hamil / Dr. Paul Pollard

Ted de Corsia
Randolph E. Branch / New Sentry

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

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

Philip Abbott
Ben Fields / Lincoln Russell

Henry Silva
Chino Rivera / General Juan Mercurio

Kent Smith
Aabel / Dr. Block

William Stevens
Policeman / Navigator Dexter

Janos Prohaska
Thetan (uncredited) / The Mikie

Geraldine Brooks
Ann Barton / Yvette Leighton