According to an interview with actor Shane Briant (Dr. Simon Helder) on the 2014 UK R2 Blu-ray, real
human blood was used in this film. Blood that could no longer be used for transfusions was sourced from the blood bank and used in the film, including in the notorious scene where Baron Frankenstein (Peter Cushing) uses his teeth to clamp down on a severed artery of the monster.
According to Shane Briant, he had an extremely hard time finding anything nice to say about the Monster's (David Prowse) costume. To this day, he calls it "plastic-y". Reportedly, when Prowse asked him what he thought of it, Briant replied: "The feet are fantastic!", upon which Prowse said: "They're mine."
This film performed poorly at the box office. Film historians cite the transition into more visceral and psychological horror over the so-called "creature features" as an important reason for its failure. Moviegoers wanted a new brand of terror "and it was 38-year old William Friedkin that gave it to them with The Exorcist (1973), and not 70-year old Terence Fisher".
This was the final film directed by Terence Fisher before his death on June 18, 1980 at the age of 76. It was also the 29th and final Hammer film that he directed. The first was Man Bait (1952).
The seventh - and last - film of Hammer's "Frankenstein" film series.