The relationship between life, death, and personhood is articulated by the body, without which there would be no such relationship to begin with. How do secular institutions and modes of knowledge understand, produce, and manage this relationship? What can this tell us about the secular and the body in its purview? As part of a larger ethnography of “American Immortalism,” I tackle these issues through a case study of “neuropreservation” in cryonics, the practice of preserving people at very low temperatures at the time of legal death with the hope that they might be revived in the future. Cryonicists are scientifically oriented secularists, and yet find themselves in frequent conflict with secular medical and legal institutions over the categories of life, death, and personhood. Whilst recent critical reevaluations of secularism focus on its entanglements with religion, these differences serve to highlight some tensions internal to the secular as they are played out in the United States. I will use the figure of the cryopreserved patient to focus on the secular body as a body produced institutionally in the interplay between law and medicine, suspended in the indeterminacies of the mind–body problem and caught in the tensions between two secular epistemologies, rationalism and materialism. What appears in this midst is speculative matter, matter that has indeterminate speculative status, but serves as a medium for speculation.