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)