A college paleontology professor acquires a newly discovered specimen of a coelacanth, but while examining it, he is accidentally exposed to its blood, and finds himself periodically turning into a murderous Neanderthal man.
| Actor | Role |
|---|---|
 Arthur FranzDonald Blake | Donald Blake |
 Joanna MooreMadeline Howard | Madeline Howard |
 Judson PrattLt. Mike Stevens | Lt. Mike Stevens |
 Troy DonahueJimmy Flanders | Jimmy Flanders |
 Nancy WaltersSylvia Lockwood | Sylvia Lockwood |
 Helen WestcottNurse Molly Riordan | Nurse Molly Riordan |
 Ross ElliottSgt. Eddie Daniels | Sgt. Eddie Daniels |
 Alexander LockwoodProf. Gilbert Howard | Prof. Gilbert Howard |
 Whit BissellDr. Oliver Cole | Dr. Oliver Cole |
 Richard H. CuttingTom Edwards - Forest Ranger | Tom Edwards - Forest Ranger |
 Hank PattersonTownsend - Night Watchman | Townsend - Night Watchman |
 Phil HarveySgt. Powell | Sgt. Powell |
 Eddie ParkerDonald as a Monster | Donald as a Monster |
 Ronnie Rondell Jr.Student | Student |
| AAnne AndersonStudent | Student |