This article explores how incurable cancer patients in the affluent Danish welfare state are recruited to clinical trials. We show that patients' impending death constitutes their potential for being configured as research subjects. To produce valuable data, patients who enroll in trials and health care professionals must engage in daily "time practices" that prolong the threshold between life and death. When death becomes inevitable, the limit of configuring dying cancer patients as research subjects is reached. Navigating this temporal logic, health care professionals balance the boundary between patients' instrumental worth as research subjects and their intrinsic worth as dying cancer patients. Whereas previous studies have critically uncovered how clinical trials operate at socioeconomic margins, we point to the ways in which clinical trials operate through temporal margins. We argue that clinical trials are dependent on configuring marginal societal spaces and marginal bodies from which to produce knowledge.