Louis Hayward ( Louis Hayward )

Philip 'Scotty' Grayson

Dennis O'Keefe ( Dennis O'Keefe )

Daniel F. O'Hara

Louise Allbritton ( Louise Allbritton )

Dr. Anastasia 'Toni' Neva

Carl Esmond ( Carl Esmond )

Dr. Ritter von Stolb

Onslow Stevens ( Onslow Stevens )

Igor Braun

Raymond Burr ( Raymond Burr )

Krebs

Art Baker ( Art Baker )

Dr. Frederick Townsend

Lowell Gilmore ( Lowell Gilmore )

Dr. William Forrest

Philip Van Zandt ( Philip Van Zandt )

Anton Radchek

Charles Evans ( Charles Evans )

Dr. Homer Allen

Frank Ferguson ( Frank Ferguson )

Carl Bemish

Reed Hadley ( Reed Hadley )

Narrator (voice)

Ray Teal ( Ray Teal )

Police Sergeant

William Tannen ( William Tannen )

FBI Chemist

Gale Storm ( Gale Storm )

Voice on Tape Recorder

Arthur Space ( Arthur Space )

Mr. North

Tamara Shayne ( Tamara Shayne )

Mrs. Ecko, the Landlady

Keith Richards ( Keith Richards )

FBI Agent Miller

Grandon Rhodes ( Grandon Rhodes )

Adolph Mizner

Steve Pendleton ( Steve Pendleton )

Police Detective Gaines

Howard Negley ( Howard Negley )

Feodore

Jimmy Lloyd ( Jimmy Lloyd )

FBI Agent Alison

Myron Healey ( Myron Healey )

FBI Agent Thompson

John Hamilton ( John Hamilton )

G.W. Hunter

Paul Bryar ( Paul Bryar )

Fred Coby ( Fred Coby )

Bert Davidson ( Bert Davidson )

Marten Lamont ( Marten Lamont )

Lee Phelps ( Lee Phelps )

Suzanne Ridgway ( Suzanne Ridgway )

Arthur Tovey ( Arthur Tovey )

Crane Whitley ( Crane Whitley )