In a context of anxiety as for the scientific progress, early bioethics did focus on moral topics: when new biomedical techniques are scientifically possible, does it mean that they are morally grounded? Early bioethics thus widely took shape around strong collaborations between medicine and moral philosophy, and admitted a subordination of the legal and practical rules to the moral standards (respect the human dignity for example), by opposition to the social or scientific standards. But with the emergence in bioethics of new trends, carried by sociologists and philosophers claiming for a new understanding of bioethics as social or political issues, the subordination of the legal and practical rules to the moral standards is widely discussed. In this context, the moral nature of bioethics is challenged: given the importance of issues around social justice and democracy in health, considering the increasing matters of conflicts of interest, doesn"t bioethics call rather a social or political reflection? The present article is focused on these topics. It examines, through an epistemological standpoint, recent developments between moral philosophy, medicine, sociology and politics in biomedical field.