Voice of the Whistler

Richard Dix

John Sinclair / John Carter

Lynn Merrick

Joan Martin Sinclair

Rhys Williams

Ernie Sparrow

James Cardwell

Fred (Doc) Graham

Tom Kennedy

Ferdinand / Hammerlock

Sam Ash

Gibson Motor Car Co. Executive (uncredited)

Egon Brecher

Dr. Rose (replaced by Frank Reicher) (uncredited)

Charles Coleman

Sinclair's Butler (uncredited)

Byron Foulger

Georgie (uncredited)

Martín Garralaga

Tony, Fruit Peddler (uncredited)

John Hamilton

Doctor (uncredited)