Stuart Gordon and Dennis Paoli originally intended to be faithful to H.P. Lovecraft's story, but the film ultimately has little in common with the story, which was intended to be a parody of "Frankenstein".
David Gale was made to shave his head and wear a toupee, as this was found to be in keeping with Dr. Hill's character. In the DVD commentary, it was revealed that this was also necessary for budgetary reasons, as there was no money available to match Gale's hair on a prosthetic head prop.
The "brains" in the severed head were made up of steer meat by-products, ground beef and fake blood and when they shot the scene in the autopsy room with the severed head being thrown out the door and then smashing onto the hallway wall, the crew were all behind the cameras with garbage bags over their clothes because no one knew just how much the brains would splatter.
According to "Re-animator: Ressurectus", the 70-minute featurette on the Limited edition two-disc "Re-animator" box set, glowstick liquid was used for the glowing green "Re-agent". It is the first time glowstick liquid/glowsticks have ever been used on film.
The bald, bearded doctor at the foot of Megan's bed who gets shoved away as Dan tries to revive her is underground cartoonist Kim Deitch ("The Boulevard of Broken Dreams"), son of legendary Jazz-era cartoonist Gene Deitch ("The Cat").
In the DVD commentary, Jeffrey Combs expressed regret over the "Who's going to believe a talking head? Get a job in a sideshow." quote, mentioning that the "talking head" part got such a laugh out of theater audiences that the "sideshow" part (his personal favorite) often went entirely unheard.