1966 Science Fiction Film (starring Raquel Welch and Creator/DonaldPleasence) about a shrinking machine used to send a mini submarine and its crew inside the body of a defecting scientist. During the UsefulNotes/ColdWar, both the United States and "[[HammerAndSickleRemovedForYourProtection The Other Side]]" have discovered the shrinking technology, with a time limit that turned it into a curiosity. But the scientist Jan Benes had discovered how to overcome the limit, and enemy agents will stop at nothing to prevent the secret from escaping from behind the Iron Curtain. Benes, wounded in an attack, is comatose and dying from a externally inoperable bloodclot, so the U.S. miniaturization taskforce organizes an expedition to be shrunken to remove the clot from the inside, operating on it at the cellular level.

But for the same reason they need to save the scientist, they have a time limit to get out of the body (or they'll grow back to normal size while inside of it). Even further, an enemy agent is trying to stop them; the protagonist Charles Grant, who smuggled the scientist from behind the Iron Curtain, has to make sure the mission succeeds while not knowing who he can trust on the crew.

The film also received a novelization by Creator/IsaacAsimov, as well as an AnimatedAdaptation. Very often [[WholePlotReference homaged or parodied]] -- see FantasticVoyagePlot.

!!This film provides examples of:

* AdaptationExpansion: The novel, big time. Besides correcting countless scientific errors, Asimov added several elements to the book that were absent in the movie. Here, Grant is a bit of a detective, essentially figuring out who TheMole is before he reveals himself, via clues [[FairPlayWhodunit available to an attentive reader]]. [[spoiler: Michaels]] is less of a traitor, and more of an obsessed pacifist -- he believes (not entirely unreasonably) that both sides are currently in balance with regard to miniaturization (*cough* mutually assured destruction *cough*), and ''either'' side having the advantage of unlimited shrinking could pressure the other side into shooting first before the new development can be used against them. Asimov also added some scenes between Grant and Benes, as well as a minor subplot about infighting between the military and scientific factions within the CMDF.
** And several years later he wrote a from-scratch "remake"-slash-"sequel", ''Fantastic Voyage 2: Destination Brain'', that attempted to clean up even more of the science and plot problems.
* AmbiguousSituation: As the novelization explicitly states, it's unclear how many of the problems the team encountered were sabotage or genuine accidents.
* ArtMajorBiology: The blood cells don't look anything like they should (they should look like tires with a membrane through the center), being essentially a closeup of a lava lamp. The heart has too many crossed fibers to efficiently pump blood (to make it look hard to find their way through the heart), etc. All of these changes were made very deliberately; the realistic versions made the film look like a voyage [[UncannyValley through a corpse]].
* BaldOfEvil: [[spoiler: Michaels]]
* BiggerOnTheInside: Played With -- The ''Proteus'' was built as a single set, with removable exterior panels to allow filming. However, some have argued that the remaining volume is insufficient for the air tanks, engines, etc.
* TheBigBoard: A vertical diagram of the scientist's body, where the location of the ''Proteus'' is marked.
* BlobMonster: The White Cells
* CommunicationsOfficer: Grant's cover
* CoolShip: The ''Proteus''
* DefectorFromCommieLand: Benes, who holds the secret to unlimited miniaturization.
* ElaborateUndergroundBase: CMDF HQ
* {{Fanservice}}: Raquel Welch is in the movie, and was 26 at the time. 'Nuff said.
* FantasticVoyagePlot: The Trope Namer
* FrickinLaserBeams: The surgical laser, it has a constant beam and slices cleanly through what it's aimed at -- but would a doctor really be using a -rifle- for brain surgery?
** When the clot to be removed is larger than himself? Very possibly.
* FutureSpandex : Under the neat white jumpsuits. Justified, both for the Fanservice, and because they're neoprene diving suits.
** FridgeBrilliance: The neoprene helps prevent dust and fibers from coming off their bodies when they swim in the bloodstream, which could be a problem when they re-enlarge.
* GovernmentAgencyOfFiction: '''C'''ombined '''M'''iniature '''D'''eterrent '''F'''orces (CMDF).
* HammerAndSickleRemovedForYourProtection: The Soviet Union and its allies are only referred to as "The Other Side".
* HighTechHexagons: The shrink ray room had hexagons all over the floor. The ship rose up on one of them once it got small enough, so that it could be shrunk one more time, and then readied for insertion into the guy's body.
* IfIWantedYouDead: In the novelization, Grant eventually figures out the identity of the mole by realizing [[spoiler:that the acts of sabotage that seem to implicate various crew members would have been far more effective if those crew members had in fact committed them using their specialized skills. The one exception is Michaels, the only one who could have mis-navigated them into a circulatory whirlpool that nearly destroyed the ship.]]
* InsufferableGenius: Duval, the surgeon.
* MegaMicrobes: Inverted -- Tiny Humans, normally sized Microbes...
* MohsScaleOfScienceFictionHardness: The movie is a 1 or 2. The novel is at least a 4, more like a 4.5 (with miniaturization instead of FTL).
** There is actually an anecdote that Asimov told the film's producers just how scientifically inaccurate it was, to which he was told [[MST3KMantra that it was just a movie]] and to just get on and write the book (though in some accounts, he was told rather less politely than recorded here).
* RaceAgainstTheClock: After miniaturization, the team has 60 minutes to complete their mission before they start to de-miniaturize.
* TheRadioDiesFirst: Technically, the ''laser'' dies first -- the wireless is cannibalized to fix it.
* SceneryPorn: The body interior sets, built full scale.
* SeekerWhiteBloodCells: White blood cells are mentioned but not seen until the near end, antibodies make a earlier appearance.
* ShrinkRay: The non-portable variety, used chiefly as a research tool due to the time limit making military uses non-viable (it's also the variety that can expand as well as shrink).
* SquareCubeLaw: Why Isaac Asimov was initially reluctant to write the novelisation -- he thought that being miniaturised was impossible because of this. Nevertheless, he decided it would make for some good writing and came up with a novelisation that is almost [[MohsScaleOfScienceFictionHardness as hard as science fiction can be]], ignoring the physical impossibility of miniaturisation.
* TenLittleMurderVictims: Who's the enemy agent on the crew that's responsible for the series of disasters threatening the mission? [[spoiler:Why, it's Dr. Michaels, the sweaty scientist played by Creator/DonaldPleasence!]]
** In the novelization, the mole is played with more subtlety. [[spoiler:Michaels avoids the blatant panic attacks of his movie incarnation, and serves as Grant's mentor about miniaturization; the two even discuss possible suspects throughout the story.]]
* ToTheBatpole: The Elevator to CMDF HQ.
* WarRoom: The CMDF Operating Theater
* WhatHappenedToTheMouse: A number of elements that should be problematic are ignored: [[spoiler:the wreckage of the ''Proteus'', and Dr. Michaels' body, after being eaten by the white blood cell -- somehow that keeps them from re-enlarging once time runs out. This is one of the most memorable plot holes of the film, and Asimov made sure to close it in his novelization.]] ''Massively'' averted by the novelization, which accurately depicts, as well as we know, what it would be like if humans could in fact be miniaturized to this degree. Even Brownian Motion (random molecular motion of a fluid or gas) is noticed and commented on. Most of the flaws of the movie are explained or elaborated on so as to be acceptable to reality, making the book as much a corrective Retcon as a novelization.
* {{Zeerust}} : Varies -- Being set TwentyMinutesIntoTheFuture in 1960s, some elements, like the laser rifle don't hold up well, while the ''Proteus'' itself varies from a sleek futuristic but practical exterior, to an interior that could be considered UsedFuture. What dates the film most of all are the '60s contemporary elements, such as computers, cars and uniforms.