Prof. Clete Ferguson

John Agar

Helen Dobson

Lori Nelson

Joe Hayes

John Bromfield

George Johnson

Robert B. Williams

Captain Lucas

Nestor Paiva

Jackson Foster

Grandon Rhodes

Lou Gibson

Dave Willock

Captain of Police

Charles Cane

The Gill Man (in water) / Lab Technician (uncredited)

Ricou Browning

Woman on Boat (uncredited)

Loretta Agar

Jennings

Clint Eastwood

Patrol Boat Dispatcher (voice / uncredited)

Bill Baldwin

First Student in Car (Driver)

Brett Halsey

The Creature (some scenes)

Ben Chapman

Photographer (uncredited)

Jere Beery

Teenager in a car

Robert Hoy

The Gill Man (on land) / Marineland Diver (uncredited)

Tom Hennesy

WNTV Newscaster

Ken Peters

Miss Abbott (uncredited)

Diane DeLaire

Policeman on Beach

Mike Doyle

Skipper (uncredited)

Jack Gargan

Mac - Spotlight Party Leader (uncredited)

Don C. Harvey

Policeman on Beach

Charles Gibb

Joe (searchlight man)

Robert Wehling

Policeman at Motel

Bill Young

Guy in Convertible

Julian Fant

Diver (uncredited)

Don House

Falling Child

Judeena Blackmer

Running Child

Sally Baskin

Police Announcer (uncredited)

Sydney Mason

Running Woman

Mildred Baskin

Dr. McCuller (uncredited)

Robert Nelson

Girl in Convertible

Patricia Powers

Search Party Member (uncredited)

Bert Stevens

Policeman (uncredited)

Charles Victor

Oceanarium Screamer

Betty Jane Howarth