Shivers. It also goes by the name of They Came From Within, which is fitting for a film that depicts weird creatures that take control of a human body and transform people into sex monsters.
The film is crude and full of inconsistencies, but it's still very effective. It's also very silly at times, but I think Cronenberg knows this and plays the film up as a black comedy. There's slapstick, there's some intentionally stupid dialogue and the scientific explanation behind all this is pure hokey, but don't let that fool you. Cronenberg's dark and disturbing vision is right behind every frame.
Trivia: the film was produced by Ivan Reitman and the special make-up effects were done by Joe Blasco!
More Overlooked Movies here. (Oh, I guess no one was compiling the links for this week!)