- Glenn Strange was playing the Frankenstein monster, but during shooting one day he tripped over a camera cable and broke his ankle. Lon Chaney Jr. (playing the Wolf Man) wasn't working that day, so he put on the Frankenstein makeup/outfit and filled in for Glenn in one scene where Dr. Mornay gets thrown through the window. So Lon Chaney wound up playing two monsters in this movie.
- Originally titled "The Brain of Frankenstein".
- As a favor, Boris Karloff did behind-the-scenes publicity work for this film. In several photos taken by Universal's publicity department, he is seen standing in line purchasing a ticket at a theater in New York City where the film is playing, and in other stills, he is shown admiring the poster art for the film outside the theater lobby.
- Lou Costello did not want to film the movie, declaring, "No way I'll do that crap. My little girl could write something better than this." A $50,000 advance in salary and the signing of he and Bud Abbott's good friend Charles T. Barton, whom some call the best Abbott and Costello director, convinced him otherwise.
- During the final chase scene, when Bud and Lou are standing in front of a door and the Frankenstein monster punches through it, Lou was off his mark and got hit on the jaw.
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