!Main characters

!!Osmosis "Ozzy" Jones
->'''Voiced by:''' Creator/ChrisRock
* CheshireCatGrin: He sports one of these every now and again.
* CoolCar: Had his cop car customized.
* CowboyCop
* DoggedNiceGuy: Has trouble winning Leah Estrogen's affections. [[spoiler: He does at the end, though.]]
* {{Determinator}}
* TheHero
* InSeriesNickname: Always known by "Ozzy".
* NiceJobBreakingItHero: He did the right thing [[spoiler: causing Frank to vomit, thereby saving him from a contaminated oyster]], but it caused Frank to lose his job and the respect of the local community, and [[NoGoodDeedGoesUnpunished got Ozzy suspended for "use of unnecessary force"]].
* OfficialCouple: With Leah at the movie's end.
* ProtagonistTitle
* RedOniBlueOni: The red to Drix's blue.
* SensitiveGuyAndManlyMan: The Manly Man to Drix's Sensitive Guy.
* SesquipedalianSmith
* ShapeshifterShowdown: What saves him against Thrax.

->'''Voiced by:''' David Hyde Pierce
* ArmCannon
* TheBigGuy
* ButNotTooWhite: Drix is played by David Hyde Pierce. The producers were ''looking'' for someone as white-bread as possible. [[Series/{{Frasier}} Niles Crane]] is about as white-bread as you can get.
* ByTheBookCop: Part of what makes him different from Osmosis.
* CaptainErsatz: Drix bears a strong resemblance to ComicBook/IronMan.
* GeniusBruiser
* AnIcePerson: His painkilling abilities are portrayed as this.
* InSeriesNickname: "Drix" is this, short for Drixenol (or Drixobenzometaphedramine).
* TheLancer
* RedIsHeroic: His main colors are red and yellow.
* RedOniBlueOni: The blue to Ozzy's red.
* SensitiveGuyAndManlyMan: The Sensitive Guy to Ozzy's Manly Man.
* TheSmartGuy: He certainly acts smarter than Osmosis, at least.

!Movie characters

->'''Voiced by:''' Creator/LaurenceFishburne
* AssKickingEqualsAuthority: He gets the bacterias to accept him as their leader after he single-handedly killed their boss.
* BadassLongcoat: One he can even use as a ''glider''.
* BerserkButton: Do not get in the way of his goal of being in the medical books. [[BadBoss He killed all of his men when one suggests they incubate]].
* BigBad: He's the reason why Frank is in danger.
* CoolShades: Owns a pair of these, and wears them frequently.
* DeadpanSnarker
* DiseasedName: And a PunnyName at that, as his name is a play on the bacteria anthrax. Justified, since he's a bacteria.
* EstablishingCharacterMoment: The first thing he does upon being introduced is to [[KickTheDog casually murder two harmless workers]], [[FamilyUnfriendlyDeath at least one in an incredibly gruesome way]]. He then proceeds to [[WalkingWasteland burn their entire boat by merely scratching its surface with his index while he is walking]].
* EvenEvilHasStandards: Is visibly disturbed upon seeing some of Frank's nightmares and bad memories.
--> '''Thrax''': (after escaping from the room) This cat was sick before I even got here!
* EvilIsPetty: Only partially. Thrax wants to kill Frank in a record time so he can be in medical textbooks.
* FamilyUnfriendlyDeath: He falls into a vat of alcohol, which of course has very deadly effects on germs... although to be fair this tends to be how irredeemable villains tend to die...
** Also applies to the first cell he kills. What he does to the bacteria mob boss too, though to a lesser degree.
* FauxAffablyEvil: He likes to hum "Fever" by Peggy Lee and presents himself as charismatic, but this barely hides the monster he is.
* FingerPokeOfDoom: Quite literally with his first victim. "Ouch."
* GloryHound: Thrax is like a serial killer who's trying to become famous in the most brutal fashion.
* PlayingWithFire: His fingernail claw burns whatever he scratches into a melting, burning lava mess.
* KnightOfCerebus: Were you expecting a movie about Chris Rock as a blood cell to have a virus in the form of a serial killer?
* NamesToRunAwayFromReallyFast: Thrax, meant to evoke ''an''thrax.
* NiceJobFixingItVillain: In the final battle with Ozzy, he use the black chain holding the hypothalamus chromosome to try and choke him. But then Shane blinks, separating the two with the chain still around Ozzy's neck. His final attack failing thanks to Ozzy's morphing abilities seal the deal.
* OmnicidalManiac: Thrax's plans involve killing people, causing the civilizations of cells in their bodies to die. The loss of life is apocalyptic at the cellular level, with an implied decimation among humans (since Thrax wants his own chapter in the medical books he'd likely seek to become an epidemic, which would entail massive loss of life).
* RedAndBlackAndEvilAllOver: Red-skinned, dressed in black, and ''definitely'' evil.
* ScaryBlackMan: Only in voice (Creator/LaurenceFishburne does it).
* SerialKiller: He keeps trophies from his victims and reminisces about them.
* ASinisterClue: Only a given, since that's the hand he uses to kill all his victims and spread his infection.
* SlasherSmile: He sports quite a few throughout the movie, the [[NightmareFace most notable one]] being when he threatens to kill Frank's daughter.
* SoftSpokenSadist: He likes to keep a low tone at times.
* VileVillainSaccharineShow: And ''how''. Apart from the serial killer overtones, there's his meeting the group of germs in the Zit. With the plan to organize coordinated assaults with the intention of causing widespread death and destruction, also spreading fear and intimidation outside Frank, Thrax comes across as a leader of a terrorist group planning an attack. It's jarring how such a vicious, murdering villain managed to stick in an otherwise light-hearted comedy.
* VillainousCheekbones: Thrax's cheekbones are so pointy they look sharp, and he his clearly evil.
* TouchOfDeath: His left index finger causes ''any'' organic matter it touches to combust or explode.
* WouldHurtAChild: Brags about killing a little girl - and has his sights on Frank's daughter when he's done with Frank.

!!Mayor Phlemming
->'''Voiced by:''' WilliamShatner
* FatIdiot: He clearly doesn't see what could happen if he keeps giving Frank junk food instead of healthy food, hence the obesity.
* HateSink: As he is designed to represent and justify Frank's poor health, he inevitably ventures into this. Notably, he abolishes Ozzy from the police force for making Frank throw up even though it was an emergency situation, fails to acknowledge Thrax as a threat despite the fact that he had killed others in the past (dismissing him as the common cold when he was one of the deadliest viruses ever), and is the only one that doesn't see the problem in giving Frank nothing but junk food.
* {{Jerkass}} : He certainly is, especially to Ozzy.
* LaserGuidedKarma: Abolished Ozzy for having Frank throw up to get out an evil virus. Then at the end when he's been booted out of office, he presses a similar button and winds up flushing himself right out of Frank's own body.
* MayorPain: Though he's not corrupt per se, he's VERY incompetent at his job and cares more about his election than anything else.
* MyGodWhatHaveIDone: Doesn't say it but his reaction as the city of Frank burns down around him pretty much has this trope all over it.
* ObstructiveBureaucrat: Let's see, he fired Osmosis and gets Drix out of Frank just for ''popping a pimple without permit'' (Which is like blowing up a building in the real world) and as mayor control's nearly all of Frank's actions, including his slovenly behavior. Said neglect needless to say, almost ends up killing the guy and every cell with him.
* SleazyPolitician: To the tee.
* TooDumbToLive: His actions almost get his city destroyed.

!!Leah Estrogen
->'''Voiced by:''' Brandy Norwood
* TheChick
* GracefulLadiesLikePurple: Her suit and even her body are both purple.
* LivingMacGuffin: Is taken hostage by Thrax, and very nearly killed by him.
* NonMammalMammaries
* OfficeLady: Works as a secretary for Mayor Phlegming.
* OfficialCouple: With Ozzy in the end.
* SassyBlackWoman
* ShesGotLegs: That mini-skirt isn't helping the fact that she has long legs.
* TheSmurfettePrinciple: Although Leah isn't the only female anthropomorphic cell in Frank's body, she's the only one with NominalImportance.
* {{Tsundere}}: Type B.
* WomenAreWiser

!!Francis "Frank" [=DiTorre=]
->'''Played by:''' Creator/BillMurray
* BumblingDad: He means well, and does care about Shane, but he has a major selfish streak. Though this is mostly due to Mayor Phlemming overriding his body for his own ends.
* ChildrenRaiseYou
* FantasticVoyagePlot: The plot takes place inside Frank's body
* FatIdiot
* GuysAreSlobs: Played straight and subverted, as in a flashback we hear Shane complain that neither he or Maggie, his wife, take care of themselves very well, Frank just got worse after Maggie died.
* TheMourningAfter: Still mourning the loss of his wife, Maggie. Justified, as it seems to be [[TooSoon a relatively recent loss]].
* OneOfTheKids
* PermaStubble
* StrawLoser
* TooDumbToLive: What kicks off the whole plot as he ''eats an egg that was inside the mouth of a monkey and got spat out onto the ground.'' [[SarcasmMode Yeah that seems sanitary]].
* VomitIndiscretionShot: Double Subverted; we don't see it actually happen (although we hear him retching, the focus is on the horrified crowd at the science fair), but we do see a picture of him puking all over Shane's teacher.

!!Shane [=DiTorre=]
->'''Played by:''' Elena Franklin
* BrokenBird
* CallingTheOldManOut: Blames Frank and his unhealthy habits for Maggie's untimely death, and calls him out for deciding to take her to a chicken wing FanConvention instead of the hiking trip she was looking forward to.
* ChildrenRaiseYou: Takes care of her dad, because he doesn't take care of himself.
* GenderBlenderName: Her first name is predominantly used by boys.
* MissingMom: Her mom died of an unspecified illness. Though it's implied she was as unhealthy as Frank has been throughout the movie.
* OnlySaneWoman: Shane often has to be the adult between her and her father.
* WomenAreWiser