In contrast to most publications on the ethics of paying research subjects, which start by identifying and analyzing major ethical concerns raised by the practice (in particular, risks of undue inducement and exploitation) and end with a set of—more or less well-justified—ethical recommendations for using payment schemes immune to these problems, this paper offers a systematic, principle-based ethical analysis of the practice. It argues that researchers have aprima faciemoral obligation to offer payment to research subjects, which stems from the principle (...) of social beneficence. This principle constitutes an ethical “spine” of the practice. Other ethical principles of research ethics (respect for autonomy, individual beneficence, and justice/fairness) make up an ethical “skeleton” of morally sound payment schemes by providing additional moral reasons for offering participants (1) recompense for reasonable expenses; and (2a) remuneration conceptualized as a reward for their valuable contribution, provided (i) it meets standards of equality, adequacy and non-exploitation, and (ii) it is not overly attractive (i.e., it does not constitute undue inducement for participation or retention, and does not encourage deceptive behaviors); or (2b) remuneration conceptualized as a market-driven price, provided (i) it is necessary and designed to help the study achieve its social and scientific goals, (ii) it does not reinforce wider social injustices and inequalities; (iii) it meets the requirement of non-exploitation; and (iv) it is not overly attractive. The principle of justice provides a strong ethical reason for not offering recompenses for lost wages (or loss of other reasonably expected profits). (shrink)