In this article, the first author provides a summary and translation from the Latin of an important early medical lecture on vampires by Nils Retzius. The lecture was delivered in Sweden, at Lund University, in 1737, and was published almost immediately thereafter. This important text has been overlooked by modern scholars of vampires. This article will bring the lecture back into circulation in its first English translation. The second author then offers an analysis of the intellectual background to this rational debunking of vampires. He demonstrates how Retzius’s attempt at a comprehensive rational explanation for vampires, typical of much Enlightenment thinking, nevertheless employs a fusion of Galenic medical thinking with more modern medical and psychosomatic notions of medicine, as well as certain Lutheran notions concerning the devil and the spirit world. His argument scotches the belief in the idea of sympathetic magic affecting the dreams of the living, while emphasising the psychosomatic effects of the imagination on the physical body.