* ActorAllusion: One episode is an AffectionateParody of ''Film/RaidersOfTheLostArk'', a movie Tom Selleck was considered to do the lead in, but gave up to do this show instead.
* TheDanza: Tom Selleck as Thomas Magnum.
* FakeBrit: John Hillerman, a native Texan, playing a retired British Army Sergeant Major -- and playing him so convincingly even ''British'' viewers thought he was a genuine Brit.
** In "Luther Gillis, File #001", Higgins insists on accompanying Gillis into a cowboy bar. When Gillis says they won't talk to a "limey", Higgins grabs Gillis by the lapels and intones "Who you callin' a ''limey'', boy?" in a broad Texas drawl. He played the whole bar scene this way.
* [[HeyItsThatGuy Hey, It's That Gal!]]: The daughter of T.C.'s friend in "A Sense Of Debt" is [[Series/BeverlyHills90210 Brenda Walsh]].
* TheOtherDarrin: DA Carol Baldwin was played by Patty [=McCormick=] in the character's first appearance and by Kathleen Lloyd in twenty episodes.
** The producers actually planned to reveal Orson Welles as Robin Masters when the series ended. Unfortunately, though, Welles died in 1985 before the storyline could materialize.
** Don Bellisario's later show ''Series/QuantumLeap'' was going to have a crossover episode, but unfortunately the ''Magnum'' series was established as existing within that show's universe, and he preferred to avoid the CelebrityParadox.
** Jack Lord was approached several times to appear on the series, but he never did (in fact, once ''Series/HawaiiFiveO'' ended he never acted again[[note]]except for a cameo in ''M Station: Hawaii'', an unsold pilot which he also executive produced[[/note]]).
* WrittenByCastMember: Roger E. Mosley co-wrote "Missing Melody," one of the few episodes of the series to focus on his character of T.C.