| Godina/e | Naslov serije ili filma | Naslov epizode | Uloga |
| 1961 | Sir Francis Drake | "The English Dragon" | Lord Oakshott |
| 1963 | The Outer Limits | "The Sixth Finger" | Gwyllm Griffiths |
| 1964 | The Outer Limits | "The Forms of Things Unknown" | Tone Hobart |
| The Great Adventure | "Kentucky's Bloody Ground" | Captain Hanning |
| The Great Adventure | "The Siege of Boonesborough" | Kapetan Hanning |
| Profiles in Courage | "John Adams" | John Adams |
| Perry Mason | "The Case of the Fifty-Millionth Frenchman" | Phillipe Bertain |
| The Travels of Jaimie McPheeters | "The Day Of The Search" | Prorok |
| 1964-1968 | The Man from U.N.C.L.E. | (stalni član postave) | Illya Kuryakin |
| 1966 | Please Don't Eat the Daisies | "Say U.N.C.L.E." | Illya Kuryakin |
| 1969 | Hallmark Hall of Fame | "Teacher, Teacher" | Hamilton Cade |
| Hallmark Hall of Fame | "The File On Devlin" | Kenneth Canfield |
| 1971 | Night Gallery | "The Phantom Farmhouse" | Dr. Joel Winter |
| The Man and the City | "Pipe Me A Loving Tune" | |
| 1972 | Colditz | (TV movie) | Poručnik Simon Carter |
| 1973 | Frankenstein: The True Story | (TV film) | Henry Clerval |
| The Six Million Dollar Man | "Wine, Women and War" | Alexi Kaslov |
| 1975-1976 | The Invisible Man | (stalni član postave) | Daniel Westin |
| 1979 | Kidnapped | | |
| 1979-1982 | Sapphire & Steel | | Steel |
| 1982 | Strike Force | "Ice" | William Hadley |
| 1983 | As the World Turns | | |
| The Return of the Man from U.N.C.L.E. | (TV film) | Illya Kuryakin |
| 1984 | The Master | "Hostages" | Castile |
| 1986 | Hammer House of Mystery and Suspense | "The Corvini Inheritance" | Frank Lane |
| Hart to Hart | "Haunted Harts" | Geoffrey Atterton |
| The A-Team | "The Say U.N.C.L.E. Affair" | Ivan |
| 1987 | Matlock | "The Billionaire" | Phil Dudley |
| 1988 | Alfred Hitchcock Presents | "Murder Party" | |
| Monsters (TV serija) | "The Feverman" | the fever man |
| 1989 | Murder, She Wrote | "From Russia...With Love" | Cyril Grantham |
| Mother Love | | Sir Alexander "Alex" Vesey |
| McCloud (TV serija) | "The Return of Sam McCloud" | Inspektor Craig |
| 1990 | Boon | "The Belles of St. Godwalds" | Simon Bradleigh |
| Lucky/Chances | (miniseries) | |
| Father Dowling Mysteries | | |
| Murder, She Wrote | "Deadly Misunderstanding" | Drew Garrison |
| 1991 | Trainer | | John Grey |
| Cluedo | | Professor Plum |
| 1993 | seaQuest DSV | "seaWest" | Frank Cobb |
| 1994 | Babylon 5 | "Infection" | Dr. Vance Hendricks |
| Titanic: The Complete Story | | Narrator |
| Heartbeat | "Arms and the Man" | Cooper |
| 1995 | VR-5 | | Dr. Joseph Bloom |
| 1996 | Mr. & Mrs. Smith | "The Impossible Mission" | Ian Felton |
| 1997 | Law & Order | "Past Imperfect" | Craig Holland |
| The Outer Limits | "Feasibility Study" | Joshua Hayward |
| 1997-1998 | Team Knight Rider | | Mobius |
| 1998 | Coming Home | (TV serial) | |
| 1999 | Sex and the City | "Shortcomings" | Duncan |
| 2000 | Deadline | "Lovers and Madmen" | Harry Hobbs |
| 2001 | The Education of Max Bickford | | Walter Thornhill |
| 2002 | Jeremiah (TV serija) | "Things Left Unsaid" | Clarence |
| 2003 | JAG | "Ice Queen (1), Meltdown (2)" | Donald "Ducky" Mallard |
| 2003-Present | NCIS | (every episode) | Donald "Ducky" Mallard |
| 2006-2009 | The Replacements | | The voice of C.A.R. |
| 2008-09 | Ben 10: Alien Force | "Paradox" and "War of the Worlds" | Paradox |
| 2009 | Batman: The Brave and the Bold | "Day of the Dark Knight!" | Merlin Ambrosius |
