| • Douglas Henderson | played | Dr. Paul Fredericks / Dr. Tillyard / Detective Lt. Runyon | 3 Episodes |
| • John Hoyt | played | Emmett Balfour / the "Bifrost" alien / Professor Hebbel | 3 Episodes |
| • Robert Culp | played | Allen Leighton / Dr. Paul Cameron / Trent | 3 Episodes |
| • Jason Wingreen | played | Fred Severn / Bill Turner / Coroner Leland | 3 Episodes |
| • Willard Sage | played | Chief of Staff / Reporter / Coulter | 3 Episodes |
| • Dabney Coleman | played | Dr. Williams / Lt. Rupert Lawrence / James Custer | 3 Episodes |
| • Edward Platt | played | Dean Radcliffe / Mr. Terence / David Hunt | 3 Episodes |
| • Robert Fortier | played | Bert Hamil / Dr. Paul Pollard / Budge | 3 Episodes |
| • Bob Johnson (1) | voiced | NORCO Intercom Voice / the Rocks / Radio Newscaster / Zanti Regent / Zanti Commander | 3 Episodes |
| • Sally Kellerman | played | Ingrid Larkin / Judith Bellero | 2 Episodes |
| • Aki Aleong | played | Dr. Su-Lin / Dr. Henry Akada | 2 Episodes |
| • Walter Burke | played | the Invisibles recruiter / Dr. Frederick Riner, MD | 2 Episodes |
| • Dabbs Greer | played | Mr. Bishop / E.F. Larkin | 2 Episodes |
| • Ivan Dixon | played | Major Harold Giles / Sgt. James Conover | 2 Episodes |
| • James Shigeta | played | Major Jong / AIO Captain Ngo Nwa | 2 Episodes |
| • Don Gordon | played | CIA Agent Luis Spain / Dr. Dave Crowell | 2 Episodes |
| • George MacReady | played | Dr. Marshall / Governor Lawrence K. Hillmond | 2 Episodes |
| • Konstantin Shayne | played | Dr. Phillip Fletcher / Murdock | 2 Episodes |
| • Gail Kobe | played | Janet Doweling / Janet Lane | 2 Episodes |
| • Henry Silva | played | General Juan Mercurio / Chino Rivera | 2 Episodes |
| • David Frankham | played | Lt. Terence "Terry" Brookman / Harvey Kry | 2 Episodes |
| • Peter Mark Richman | played | Physicist Ian Frazer / Jefferson Rome | 2 Episodes |
| • Kent Smith | played | Dr. Block / Aabel | 2 Episodes |
| • Ted de Corsia | played | Second Sentry / Randolph Branch | 2 Episodes |
| • Read Morgan | played | Poker Dealer (Uncredited) / Adam Link | 2 Episodes |
| • Scott Marlowe | played | Jory Peters / Andre | 2 Episodes |
| • Shirley O'Hara | played | Dr. Soldini / Receptionist | 2 Episodes |
| • Crahan Denton | played | Sheriff Simon Stakefield / Dr. Matthew James | 2 Episodes |
| • Martin Landau | played | Professor Andro / Richard Bellero, Jr | 2 Episodes |
| • David McCallum | played | Gwyllm Griffiths / Tone Hobart | 2 Episodes |
| • Curt Conway (1) | played | Dr. Philip Mendl / Franklin Karlin | 2 Episodes |
| • Tim O'Connor | played | Clint Anderson / Paul Tanner | 2 Episodes |
| • James Sikking | played | the Orderly / Botany | 2 Episodes |
| • Nellie Burt | played | the Wife of Justice / Ethel Latimer | 2 Episodes |
| • Ben Wright | played | General Benton / Philip Exeter Dundee | 2 Episodes |
| • Joan Camden | played | Ann Pearson / Prof. Stephanie Linden | 2 Episodes |
| • Paul Lukather | played | Official / Ed Nichols | 2 Episodes |
| • Robert Duvall | played | Louis Mace / Adam Ballard | 2 Episodes |
| • Leonard Nimoy | played | Konig / Judson Ellis | 2 Episodes |
| • Jacqueline Scott | played | Caroline Maxwell / Anthropologist Alicia Hendrix | 2 Episodes |
| • Geraldine Brooks | played | Yvette Leighton / Ann Barton | 2 Episodes |
| • Robert Doyle (1) | played | Wilt Morgan / Mark Lake | 2 Episodes |
| • Rudy Solari | played | Griffin / Captain Jack Buckley | 2 Episodes |
| • Kim Hector | played | Johnny Subiron | 2 Episodes |
| • Noel de Souza | played | Dr. Sung / Captain Fortunato | 2 Episodes |
| • Allyson Ames | played | Loreen / Arndis Pollard | 2 Episodes |
| • Marlowe Jensen | played | the Minister / Sgt. Berry | 2 Episodes |
| • Bill Hart | played | Corporal Delano / Durn | 2 Episodes |
| • William Douglas (1) | played | The Galaxy Being / O.B.I.T. Creature | 2 Episodes |