Chris Rock

Osmosis Jones (voice)

Laurence Fishburne

Thrax (voice)

David Hyde Pierce

Drix (voice)

Brandy Norwood

Leah (voice)

William Shatner

Mayor Phlegmming (voice)

Ron Howard

Tom Colonic (voice)

Kid Rock

Kidney Rock (voice)

Bill Murray

Frank Detorre

Molly Shannon

Mrs. Boyd

Chris Elliott

Bob

Elena Franklin

Shane Detorre

Jonathan Adams

Officer Tom (voice)

Carlos Alazraqui

Spanish Germ (voice)

Eddie Barth

Conductor (voice)

Sally Brooks

Additional Character Voices (voice)

Rodger Bumpass

Joe Cramp / Announcer for Nerve News Network (voice)

Janis Dardaris

Additional Character Voices (voice)

Antonio Fargas

Chill the Flu Shot (voice)

Eddie Frierson

Frank Police Department Officer (voice)

Donald Fullilove

Doughnut (voice)

Jackie Gonneau

Additional Character Voices (voice)

Richard Steven Horvitz

Additional Character Voices (voice)

Rif Hutton

Charlie (voice)

Anne Lockhart

Female Red Blood Cell (voice)

Sherry Lynn

Trudy (voice)

Danny Mann

Musician Cell (voice)

Mickie McGowan

Brain Librarian (voice)

Joel Silver

Police Chief (voice) (uncredited)

John Melendez

Artie (voice)

Héctor Mercado

Additional Character Voices (voice)

Paul Pape

Male Red Blood Cell #2 (voice)

Chris Phillips

Firefighter Doug (voice)

Al Rodrigo

Frank Police Department Walkie Talkie (voice)

Herschel Sparber

Bruiser (voice)

Keri Tombazian

Additional Character Voices (voice)

Paul Tuerpe

Additional Character Voices (voice)

Robert Wisdom

Big Germ (voice)

Danny Murphy

Zookeeper Superintendent

Jackie Flynn

School Janitor

Abe Farrelly

Bus Girl #2

Kevin J. Flynn

Docky's Clamshack Waiter

Sean Gildea

Dreamy Photographer

Nikki Tyler-Flynn

Nurse #2

Zen Gesner

ER Doctor #1

Zak Penn

ER Doctor #3