Husband and wife Ralph Bates and Virginia Wetherell first met in this film as they prepared to shoot the scene in it in which Bates (as Dr. Jekyll) kills a prostitute (played by Wetherell).
Martine Beswick has said that she agreed to go topless when she took the role, but during filming director Roy Ward Baker said she should do a full-frontal shot. Beswick did not want to do so, and they argued over it so much they did not speak to each other for a week. They finally made up and Beswick ended up agreeing to be fully nude, but they could only show her breasts and buttocks on screen, not her pubic hair. In order to do that, she would still have to strip totally naked on set. She demanded a closed set, which the director agreed to do, but she remembered seeing "dozens of people hanging from the rafters" in the studio during the shoot to look at her.
After starring in Violence et sexe aux temps préhistoriques (1971) for Hammer, Penthouse Pet Julie Ege was offered the role of Sister Hyde, which she turned down. After appearing nude in a previous film, she was reluctant to do more nude scenes, though she ended up doing them in later films in order to get cast.
Also released in the same year by Hammer was the film La Fille de Jack l'Éventreur (1971), which also had a Jack the Ripper story, thereby making two "Jack the Ripper' films from Hammer in the same year.
Actor Ralph Bates was touted as one of Hammer's rising stars when James Carreras ventured in 1969 that "Lee and Cushing are getting a bit long in the tooth. We have a new boy here named Ralph Bates." Carreras 'discovered' Bates after seeing him play Caligula in Granada Television's drama series The Caesars (1968). Director Peter Sasdy then chose him for Hammer's Une messe pour Dracula (1970), he played the lead role in Les horreurs de Frankenstein (1970), and stepped in to replace Peter Cushing when his wife Helen fell ill just before production on La soif du vampire (1971). He was their immediate choice to play Dr. Jekyll in this film, even though he was never under contract to the studio. Enjoying his time at Hammer immensely, he went from "picture to picture" and "in 18 months I turned around and realized I had done five pictures in a row. I just got sucked in."