Arthur Franz as Donald Blake

Joanna Moore as Madeline Howard

Judson Pratt as Lt. Mike Stevens

Troy Donahue as Jimmy Flanders

Nancy Walters as Sylvia Lockwood

Helen Westcott as Nurse Molly Riordan

Ross Elliott as Sgt. Eddie Daniels

Alexander Lockwood as Prof. Gilbert Howard

Whit Bissell as Dr. Oliver Cole

Richard H. Cutting as Tom Edwards - Forest Ranger

Hank Patterson as Townsend - Night Watchman

Phil Harvey as Sgt. Powell

Eddie Parker as Donald as a Monster

Ronnie Rondell Jr. as Student

Anne Anderson as Student