Actor-network theory has, until recently, narrated the co-evolution of science and society in terms of dramatic triumphs and betrayals. This paper attempts to incorporate 'ambivalence' into the process of enrolment and black-boxing so central to the construction and continuation of actor-networks. Though ambivalence towards one's own and others' attributed roles in the network would seem to threaten the integrity of a given network, we suggest that it might reinforce it. Drawing upon fieldwork on the UK Cervical Screening Programme (CSP), we show how General Practitioners seriously problematize their own roles and the black-boxed status of the Cervical Smear Test within the CSP network. However, we also show that it is this very problematization that serves to render the network durable and workable.