Matthew Modine

as Thomas P. Johnson / Voice of Fluke

Nancy Travis

as Carol Johnson

Eric Stoltz

as Jeff Newman

Max Pomeranc

as Brian Johnson

Ron Perlman

as Sylvester

Jon Polito

as Boss

Bill Cobbs

as Bert

Federico Pacifici

as Prof. Santini

Clarinda Ross

as Jane, Tom's Secretary

Adrian Roberts

as Night Guard

Bart Hansard

as Day Guard

Deborah Hobart

as Dogpound Vet

Libby Whittemore

as Libby, the Housekeeper

Collin Wilcox Paxton

as Bella

Samuel L. Jackson

as Rumbo (voice)

Sam Gifaldi

as Young Fluke (voice)

Comet

as Fluke

Barney

as Rumbo