- William Osler - Mu Lambda 165 (aka: Host Computer)
- William Osler - Computer voice & Host
- Ed Ames - Mr. Smith
- Sterling Hayden - Old Jeremiah
- George Sperdakos - Jubal
- Gillie Fenwick - Old Abraham
- Sean Sullivan - Rachel's Father
- Aileen Seaton - Rachel's Mother
- James Barron - Garth's Father
- Kay Hawtrey - Garth's Mother
- Scott Fisher - Small Boy
- Walter Koenig - Oro
- Alexandra Bastedo - Idona
- Stephen Young - Dr. Chris
- Frank Converse - Dr. Gerald W. Aaron
- John Colicos - The Governor
- Barry Morse - Shaliff
- Lloyd Bochner - Col. M.P. Garoway
- Susan Stacey - Five
- Simon Oakland - Dr. Asgard
- Percy Rodriguez - Sakharov Richards
- Angel Tompkins - Daphne
- Donnelly Rhodes - Roloff
- Henry Beckman - William
- Edward Andrews - Linus Farthing
- William Hutt - Dr. Pete Marshall
- Antoinette Bower - Dr. Heather Marshall
- Ivor Barry - Chief Rathe Masters
- Doug McGrath - Sergeant
- Vivian Reis - Jane
- Clive Endersby - 1st Tube Dweller
- Ray Fitzwalter
- Leo Orenstein
- Harvey Hart
- George McCowan
- Joseph L. Scanlan
- Shimon Wincelberg
- John Meredyth Lucas
- Douglas Hall
- Don Wallace
- Paul Schneider
- Norman Klenman
- Ed Richardson
- Derrett Lee
- Douglas Trumbull
- Gerry Rochon
- Mary Lou Fraser
- Barrie Diehl
- Wally Weaver
- Wallie Harris
- Doug Drew
- Bob Kozak
- Malcolm Fox
Keir Dullea hace el papel de Devon.
Robin Ward interpreta a Garth en la serie.
Gay Rowan hace el papel de Rachel.
William Osler hace el papel de Mu Lambda 165 (aka: Host Computer).
Capítulo disponible en las siguientes plataformas:
