- Bela Lugosi
- Dr. Alex Zorka
- Robert Kent
- Capt. Bob West
- Dorothy Arnold
- Jean Drew
- Edwin Stanley
- Dr. Fred Mallory
- Regis Toomey
- Jim Daly
- Jack C. Smith
- Monk
- Edward Van Sloan
- Jarvis [Chs. 2-12]
- Dora Clement
- Ann Zorka [Chs. 1-2]
- Anthony Averill
- Rankin - Henchman [Chs. 2-12]
- Hugh Huntley
- Perkins - Mallory's Lab Assistant [Chs. 2-12]
- Monte Vandergrift
- Al - Guard [Ch. 5]
- Frank Mayo
- Train Engineer [Ch. 6]
- Jim Farley
- Skipper [Ch. 9]
- Eddie Acuff
- Mac - AMI Agent [Chs. 2-12]
- Reed Howes
- Signalman [Ch. 10]
- Ed Wolff
- The Robot
- Hooper Atchley
- Experimental Lab Tech
- Roy Barcroft
- Parker - AMI Agent
- Robert Blair
- Smith
- Al Bridge
- White Rose Sailor
- Don Brodie
- Thug
- Lane Chandler
- Henchman with Rankin
- Edmund Cobb
- Army Sergeant
- Lee J. Cobb
- Road Crew Foreman
- Eddie Dunn
- Policeman
- Jerry Frank
- Henchman with Rankin
- Karl Hackett
- Brown
- Charles King
- Cop
- George Magrill
- Thug-Pilot / Schooner Crewman (uncredited)
- Monte Montague
- Airplane Mechanic
- Pat O'Malley
- AMI Chief
- David Sharpe
- Schooner Sailor
- Tom Steele
- Train Conductor / Radio Truck Driver (uncredited)
- Forrest Taylor
- Black
- Harry Wilson
- Schooner Crewman
