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