Merton’s early work on the ambivalence of scientists illustrates the productivity of importing a psychological concept to sociology. For commentators on the experience of modern societies, ambivalence describes the contradictory affective dimension of late modernity. In this article, our aim is to understand the extent to which sociological ambivalence reveals the contradictory relations between two orders of scientific knowledge: the epistemic and the social order. We illustrate several sorts of ‘value tensions’ in psychiatric genetics, a domain where the search for biological causes has led to several important shifts in scientific reasoning. For scientists working at a major UK research centre, we show how these tensions have transformed the organization of the scientific community; ambivalence is both a reflexive and uncomfortable response to a new way of producing knowledge. We argue that tension and ambivalence are intrinsic aspects of science-making and may reflect processes other than revolution and totalizing transformation.