Osmosis Jones: A Farrelly Brothers movie about a total slob Frank (Bill Murray) who catches a variety of anthrax, represented by Thrax (Laurence Fishburne), the bad guy of the movie. It's up to a loner "cop" (white blood cell) and his cold tablet buddy Drix(Chris Rock and David Hyde Pierce, respectively) to track down and eliminate the no-good virus.

The movie takes place 1/4 in live action, with Bill Murray and Chris Elliott (playing his buddy Bob) playing out some good laughs.

The remainder takes place in the fascinating animated view of the interior of Frank's body, with the characters and settings having an awesome amorphous quality that is (In my experience anyway) fairly unique as an animated technique.

Chris Rock is always hilarious, as is the straight man David Hyde Pierce.
Also funny are some of the little touches, like the cars having cilia instead of wheels, signs reading "No Cilia, No Cytoplasm, No Service" on the wall of restaurants, etc.

There are some downsides, since this is typical Farrelly Brothers fare, it lacks any sophistication, not to mention the fact that Thrax is repeatedly referred to as a virus, even though anthrax is technically a spore-forming bacterium. But nitpicking aside, I'd recommend this movie to anyone who appreciates animated film styles, Chris Rock style comedy, or the Farrelly Brothers.

IMDB:

Full Cast for Osmosis Jones(2001)

Directed by
Bobby Farrelly
Peter Farrelly

Writing credits (WGA)
Marc Hyman (written by)

Cast (in credits order)
Chris Rock .... Osmosis Jones (voice)
Laurence Fishburne .... Thrax (voice)
David Hyde Pierce .... Drix (voice)
Brandy Norwood .... Leah (voice)
William Shatner .... Mayor Phlegmming (voice)
Molly Shannon .... Mrs. Boyd
Chris Elliott (I) .... Bob
Bill Murray .... Frank Pepperidge
Joel Silver .... The Chief (voice)
rest of cast listed alphabetically
Joe C. .... White Blood Cell (voice)
Elizabeth Farrelly Jordan .... Nurse
Anna Farrelly
Kathy Farrelly .... Nurse
Kevin J. Flynn
Nicki Tyler Flynn .... Nurse
Elena Franklin .... Shane
Zen Gesner .... Doctor
Evan Hoffman
Ron Howard
Kelsey Jordan
Thomas Jordan
Kid Rock .... White Blood Cell (voice)
Cortney Urichuck .... Student (uncredited)
Megan Urichuck .... Student (uncredited)