In this paper we pull together an analysis of power with an analysis of the agency of a Professional Association of Pharmacists in the building of an electronic prescription (EP) system. We frame our analysis of the building process of an EP system in terms of power from the perspective of the pharmacists collective, and particularly, from the perspective of the Catalan Professional Association of Pharmacists (CPAP). What concerns us in this paper is the role of the CPAP in structuring the field of other’s action –namely, community pharmacies which are members of the CPAP and the Catalan Health Service– during the building process. From this perspective, we study power not only in the CPAP’s capacity to influence others through the control of resources that others need, but also in the field of relations that characterize a power arena and in the effect of the ordering work performed by the CPAP. By examining the case from the lens of the circuits of power we identify two kinds of interventions from the CPAP –conservative and transformative–, and distinguish them based on the circuit of power they active and the use of IT they make.