Abstract. A recurrent theme in ethnomethodological research is that of"instructed actions". Contrary to the classic traditions in the social and cognitive sciences, which attribute logical priority or causal primacy to instructions, rules, and structures of action, ethnomethodologists investigate the situated production of actions which enable such formulations to stand as adequate accounts. Consequently, a recitation of formal structures can not count as an adequate sociological description, when no account is given of the local production of what those structures describe. The natural sciences can be described as a domain of practical action in which the use of methods enables the intersubjective reproduction of naturalistic observations and experiments. As numerous sociological studies of laboratory practices have shown, the achievement of intersubjective order cannot be reduced to formal methods; instead, it arises from the work of custom-fitting relevant methods to the local circumstances of the research. In this paper we discuss a possible extension of this idea to cover two intertwined aspects of molecular biology: (1) the work of following instructions on how to perform routine laboratory procedures, and (2) the relationship between cellular orders and the encoded 'instructions' contained in the DNA molecule. We suggest that a "classic" conception of scientific action is implied by the way formal instructions are treated as a primary basis, both for molecular biologists' actions and the cellular functions they study, and we envision an ethnomethodological alternative to those conceptions of social and biological order.For the last several years, we have investigated the production and dissemination of routine laboratory techniques in molecular biology. These include plasmid purification and isolation (commonly called "the plasmid prep") and the polymerase chain reaction (PCR). I In the course of these investigations we interviewed practitioners in several scientific, medical and forensic laboratories. These practitioners described how they performed the procedures, and in a few cases taught us how to do elementary routines. We also collected numerous written and verbal accounts which described problems associated with different applications of the techniques. By focusing on these techniques, we gained a precise understanding of how the skills, protocols, instruments, and materials associated with a 'same' practical object (viz., a technique described, and sometimes patented, under an identical name or trademark) were configured under different circumstances. We pursued ques-