
| Boris Karloff | ... | Gruesome |
 | Ralph Byrd | ... | Dick Tracy |
 | Anne Gwynne | ... | Tess Truehart |
 | Edward Ashley | ... | Dr. Lee Thal |
 | June Clayworth | ... | Dr. I.M. Learned (Irma), Prof. Tomic's Assistant |
 | Lyle Latell | ... | Pat Patton, Plainclothesman |
 | Tony Barrett | ... | 'Melody' Fiske |
 | Skelton Knaggs | ... | X-Ray |
 | James Nolan | ... | Dan Sterne, Newspaper Reporter (as Jim Nolan) |
 | Joseph Crehan | ... | Chief Brandon |
 | Milton Parsons | ... | Dr. A. Tomic, State U. Physicist |
| rest of cast listed alphabetically: |
 | Ernie Adams | ... | Bartender at Hangman's Knot (uncredited) |
 | Phil Arnold | ... | Sneezing Bank Customer (uncredited) |
 | Lex Barker | ... | City Hospital Driver (uncredited) |
 | Eddie Borden | ... | Bank customer (uncredited) |

| Robert Bray | ... | Sarge (Cop at Tracy's) (uncredited) |
 | Robert Clarke | ... | Fred, police analyst (uncredited) |
 | George Cooper | ... | Stone, bank teller (uncredited) |
 | Suzi Crandall | ... | Blonde Customer (uncredited) |
 | William Gould | ... | 'Pop', hospital Desk Sergeant (uncredited) |
 | Ben Hall | ... | Luke - Police Stooge (uncredited) |
 | Harry Harvey | ... | Humphrey, Bank guard (uncredited) |
 | Tom Keene | ... | Dr. Frankey (uncredited) |
 | George Lloyd | ... | Manager of the 'Hangmans Knot' (uncredited) |
 | Robert Malcolm | ... | Dr. Carver (police doctor) (uncredited) |
 | Sean McClory | ... | Officer Carney (uncredited) |
 | Lew Meehan | ... | Police Driver in montage (uncredited) |
 | Bruce Mitchell | ... | Police Sgt. in montage (uncredited) |
 | Lee Phelps | ... | Detective in Car (uncredited) |
 | Lorin Raker | ... | Insolvent Bank Customer (uncredited) |
 | Bert Roach | ... | Crandall, a bank customer (uncredited) |
 | Jason Robards Sr. | ... | Mr. Fax, 1st National Bank V.P. (uncredited) |
 | Harry Strang | ... | Tim, Tracy's Hospital Guard (uncredited) |
 | Tex Swan | ... | Policeman (uncredited) |