John Agar
Prof. Clete Ferguson
Lori Nelson
Helen Dobson
John Bromfield
Joe Hayes
Nestor Paiva
Captain Lucas
Grandon Rhodes
Jackson Foster
Dave Willock
Lou Gibson
Robert B. Williams
George Johnson
Charles Cane
Police Captain
Loretta Agar
Woman on Boat (uncredited)
Bill Baldwin
Patrol Boat Dispatcher (voice / uncredited)
Jere Beery
Photographer (uncredited)
Ricou Browning
The Gill Man (in water) / Lab Technician (uncredited)
Diane DeLaire
Miss Abbott (uncredited)
Mike Doyle
Cop (uncredited)
Clint Eastwood
Jennings (uncredited)
Jack Gargan
Skipper (uncredited)
Charles Gibb
Cop (uncredited)
Brett Halsey
Pete (uncredited)
Don C. Harvey
Mac - Spotlight Party Leader (uncredited)
Tom Hennesy
The Gill Man (on land) / Marineland Diver (uncredited)
Don House
Diver (uncredited)
Robert F. Hoy
Charlie (uncredited)
Ned Le Fevre
Newscaster (uncredited)
Sydney Mason
Police Announcer (uncredited)
Robert Nelson
Dr. McCuller (uncredited)
Patricia Powers
Girl in Convertible
Bert Stevens
Search Party Member (uncredited)
Charles Victor
Policeman (uncredited)
Robert Wehling
Joe (uncredited)
James R. Wolfe
Man at Tank (uncredited)