Koji Furuhata earned the role of Frankenstein through an open audition. Furuhata wore green contact lenses to emulate a Caucasian look, a flat-head prosthetic and brow resembling Jack Pierce's Frankenstein Monster design and large shirts and loincloths. Honda had originally wanted to explore more of the science-gone-wrong theme, but was forced to change the story in the middle to reach a climactic monster battle. Nick Adams delivered all of his lines in English, while everyone else delivered their lines in Japanese.