In this paper, we use a scientific controversy, and the efforts to legitimize and undermine a theory, to examine the co-production of facts and the rules for verifying facts over time. We discuss these processes in terms of what we call 'styles of scientific practice.' In contrast to the focus of idealist philosophers on theory production and validation as forms of logic or ways of thinking, our styles of practice also include the activities of hands and eyes and the discourses between multiple actors in diverse situations. We discuss aspects of the different styles of practice deployed by opponents in a current controversy surrounding the etiology of AIDS to understand how the same data are interpreted in different ways to support diametrically opposed views. Our study describes and examines rules of confirmation used by supporters of the theory that HIV causes AIDS. For example, we introduce an 'epidemiological' style of practice used by AIDS researchers to synthesize information to understand this disease. Styles of practice stress the historically located collective efforts of scientists, technicians, administrators, institutions, and various 'publics' as they build and sustain ways of knowing. Yet, we also show that the 'history' is also a contested construction, not a given in dusty archives. We describe the different versions of history constructed by various participants in the debate to validate their current constructions and definitions of the disease AIDS. Finally, we discuss the politics behind disease definitions and the consequences of different definitions.
